Homematic: GUI inaccessible (404 Error)

Dear community,
since some days, I can´t reach the GUI of Homematic anymore. It´s just showing a 404 Error. The integration seems to be alive, as homematic entities are still present and delivering reasonable values.
Now, I switched back to system snapshot 14 days ago (hass. At that time the homematic GUI was definitely present. Unfortunately, this didn´t help - I´m still getting a 404 Error instead of the GUI.
Now, I don´t what to try next - I´m happy for any hint! (Google didn´t help either, the only similar problm I found was from 2018 with older hass-versions; these problems were fixed, so it´s not comparable to what I have)
Here is some data on my system (after downgrading to the older snaphost):

System Health

Home Assistant Core Integration

version: 0.118.5
installation_type: Home Assistant OS
dev: false
hassio: true
docker: true
virtualenv: false
python_version: 3.8.6
os_name: Linux
os_version: 5.4.79-v8
arch: aarch64
timezone: Europe/Berlin

Home Assistant Cloud

logged_in: false
can_reach_cert_server: ok
can_reach_cloud_auth: ok
can_reach_cloud: ok

Hass.io

host_os: Home Assistant OS 5.9
update_channel: stable
supervisor_version: 2020.12.7
docker_version: 19.03.13
disk_total: 28.6 GB
disk_used: 10.3 GB
healthy: true
supported: true
board: rpi4-64
supervisor_api: ok
version_api: ok
installed_addons: Samba share (9.3.0), SSH & Web Terminal (7.8.0), Visual Studio Code (2.9.1), Glances (0.9.1), Node-RED (7.2.11), AdGuard Home (2.6.1), InfluxDB (3.7.9), Grafana (5.3.6), Portainer (1.3.0), HomeMatic CCU (10.3)

Lovelace

dashboards: 1
mode: storage
views: 12
resources: 3

And here is the log of the homematic integration - unfortunately I´m not able to interpret it properly:

at [email protected]/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2123)
	at [email protected]/java.util.concurrent.LinkedBlockingQueue.poll(LinkedBlockingQueue.java:458)
	at app//de.eq3.ccu.virtualdevice.service.internal.rega.VirtualDeviceHandlerRega.registerCallback(VirtualDeviceHandlerRega.java:99)
	at [email protected]/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at [email protected]/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at [email protected]/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at [email protected]/java.lang.reflect.Method.invoke(Method.java:566)
	at app//de.eq3.cbcs.legacy.communication.rpc.internal.rpc.AnnotationAwareRpcHandler.execute(AnnotationAwareRpcHandler.java:80)
	at app//de.eq3.ccu.server.internal.RpcMessageHandler.handle(RpcMessageHandler.java:70)
	at app//de.eq3.ccu.server.internal.RpcMessageHandler.handle(RpcMessageHandler.java:24)
	at app//io.vertx.core.eventbus.impl.HandlerRegistration.deliver(HandlerRegistration.java:212)
	at app//io.vertx.core.eventbus.impl.HandlerRegistration.handle(HandlerRegistration.java:191)
	at app//io.vertx.core.eventbus.impl.EventBusImpl.lambda$deliverToHandler$3(EventBusImpl.java:505)
	at app//io.vertx.core.eventbus.impl.EventBusImpl$$Lambda$126/0xeef7f028.handle(Unknown Source)
	at app//io.vertx.core.impl.ContextImpl.lambda$wrapTask$2(ContextImpl.java:337)
	at app//io.vertx.core.impl.ContextImpl$$Lambda$102/0xed17da28.run(Unknown Source)
	at app//io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
	at app//io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403)
	at app//io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:445)
	at app//io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858)
	at [email protected]/java.lang.Thread.run(Thread.java:834)
Dec 29, 2020 8:25:30 AM io.vertx.core.impl.BlockedThreadChecker
WARNING: Thread Thread[vert.x-eventloop-thread-4,5,main] has been blocked for 8316 ms, time limit is 2000
io.vertx.core.VertxException: Thread blocked
	at [email protected]/jdk.internal.misc.Unsafe.park(Native Method)
	at [email protected]/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:234)
	at [email protected]/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2123)
	at [email protected]/java.util.concurrent.LinkedBlockingQueue.poll(LinkedBlockingQueue.java:458)
	at app//de.eq3.ccu.virtualdevice.service.internal.rega.VirtualDeviceHandlerRega.registerCallback(VirtualDeviceHandlerRega.java:99)
	at [email protected]/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at [email protected]/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at [email protected]/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at [email protected]/java.lang.reflect.Method.invoke(Method.java:566)
	at app//de.eq3.cbcs.legacy.communication.rpc.internal.rpc.AnnotationAwareRpcHandler.execute(AnnotationAwareRpcHandler.java:80)
	at app//de.eq3.ccu.server.internal.RpcMessageHandler.handle(RpcMessageHandler.java:70)
	at app//de.eq3.ccu.server.internal.RpcMessageHandler.handle(RpcMessageHandler.java:24)
	at app//io.vertx.core.eventbus.impl.HandlerRegistration.deliver(HandlerRegistration.java:212)
	at app//io.vertx.core.eventbus.impl.HandlerRegistration.handle(HandlerRegistration.java:191)
	at app//io.vertx.core.eventbus.impl.EventBusImpl.lambda$deliverToHandler$3(EventBusImpl.java:505)
	at app//io.vertx.core.eventbus.impl.EventBusImpl$$Lambda$126/0xeef7f028.handle(Unknown Source)
	at app//io.vertx.core.impl.ContextImpl.lambda$wrapTask$2(ContextImpl.java:337)
	at app//io.vertx.core.impl.ContextImpl$$Lambda$102/0xed17da28.run(Unknown Source)
	at app//io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
	at app//io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403)
	at app//io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:445)
	at app//io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858)
	at [email protected]/java.lang.Thread.run(Thread.java:834)
Dec 29, 2020 8:25:31 AM io.vertx.core.impl.BlockedThreadChecker
WARNING: Thread Thread[vert.x-eventloop-thread-4,5,main] has been blocked for 9316 ms, time limit is 2000
io.vertx.core.VertxException: Thread blocked
	at [email protected]/jdk.internal.misc.Unsafe.park(Native Method)
	at [email protected]/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:234)
	at [email protected]/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2123)
	at [email protected]/java.util.concurrent.LinkedBlockingQueue.poll(LinkedBlockingQueue.java:458)
	at app//de.eq3.ccu.virtualdevice.service.internal.rega.VirtualDeviceHandlerRega.registerCallback(VirtualDeviceHandlerRega.java:99)
	at [email protected]/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at [email protected]/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at [email protected]/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at [email protected]/java.lang.reflect.Method.invoke(Method.java:566)
	at app//de.eq3.cbcs.legacy.communication.rpc.internal.rpc.AnnotationAwareRpcHandler.execute(AnnotationAwareRpcHandler.java:80)
	at app//de.eq3.ccu.server.internal.RpcMessageHandler.handle(RpcMessageHandler.java:70)
	at app//de.eq3.ccu.server.internal.RpcMessageHandler.handle(RpcMessageHandler.java:24)
	at app//io.vertx.core.eventbus.impl.HandlerRegistration.deliver(HandlerRegistration.java:212)
	at app//io.vertx.core.eventbus.impl.HandlerRegistration.handle(HandlerRegistration.java:191)
	at app//io.vertx.core.eventbus.impl.EventBusImpl.lambda$deliverToHandler$3(EventBusImpl.java:505)
	at app//io.vertx.core.eventbus.impl.EventBusImpl$$Lambda$126/0xeef7f028.handle(Unknown Source)
	at app//io.vertx.core.impl.ContextImpl.lambda$wrapTask$2(ContextImpl.java:337)
	at app//io.vertx.core.impl.ContextImpl$$Lambda$102/0xed17da28.run(Unknown Source)
	at app//io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
	at app//io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403)
	at app//io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:445)
	at app//io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858)
	at [email protected]/java.lang.Thread.run(Thread.java:834)
172.30.32.2 - - [29/Dec/2020:08:29:19 +0100] "GET / HTTP/1.1" 200 1116 "http://192.168.168.39:8123/core_homematic" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
172.30.32.2 - - [29/Dec/2020:08:29:19 +0100] "GET /pages/index.htm&client=3 HTTP/1.1" 302 0 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
172.30.32.2 - - [29/Dec/2020:08:29:19 +0100] "GET /pages/index.htm?sid=@gluMsHd94t@ HTTP/1.1" 404 256 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
2020-12-29 08:29:33,969 [INFO] DeviceBackgroundUpdateSubsystem - SYSTEM: 0 Accesspoints in Queue
2020-12-29 08:29:33,970 [INFO] DeviceBackgroundUpdateSubsystem - SYSTEM: Permanent-/Burstlistener Handler utilization: 0/50 used

Last not least, my homematic configuration (which worked fine so far):

rf_enable: false
wired_enable: false
hmip_enable: true
rf:
  - type: CCU2
    device: /dev/ttyAMA0
wired:
  - serial: xy
    key: abc
    ip: 192.168.0.0
hmip:
  - type: HMIP_CCU2
    device: /dev/ttyUSB0
regahss_reset: false

Just found an open thread with my problem described above on the GitHub project page (was obviously too tired to find this last night)
https://github.com/home-assistant/addons/issues/1725
Anyway, it´s not solved, so I´m still happy for your help!