Having the same issue…hassio on a pi4 wired with DHCP static reservation. The interesting part is that I can access HA from my phone and work laptop (both on same wifi network) but not from personal laptop also on same wifi network, both laptops with same OS.
This is the route table output from laptop that fails:
Destination Gateway Flags Netif Expire
192.168.x.x dc:a6:32:69:49:xx UHLWIi en0 1184
And this from laptop that works:
Destination Gateway Flags Netif Expire
192.168.x.x dc:a6:32:69:49:xx UHLWIi en0 1188
Also VERY interesting, nmap sees some services open but tcp/8123 appears to be a filtered port (e.g. behind a firewall) – WTH?
Starting Nmap 7.80 ( https://nmap.org ) at 2020-07-09 13:16 EDT
Nmap scan report for 192.168.x.x
Host is up (0.0041s latency).
PORT STATE SERVICE
8123/tcp filtered polipo
MAC Address: DC:A6:32:69:49:xx (Raspberry Pi Trading)
Nmap done: 1 IP address (1 host up) scanned in 0.31 seconds
Starting Nmap 7.80 ( https://nmap.org ) at 2020-07-09 13:14 EDT
Nmap scan report for 192.168.x.x
Host is up (0.0046s latency).
Not shown: 8973 filtered ports
PORT STATE SERVICE
22/tcp closed ssh
25/tcp closed smtp
53/tcp closed domain
80/tcp closed http
88/tcp closed kerberos-sec
110/tcp closed pop3
139/tcp open netbios-ssn
143/tcp closed imap
389/tcp closed ldap
443/tcp closed https
445/tcp open microsoft-ds
465/tcp closed smtps
587/tcp closed submission
636/tcp closed ldapssl
993/tcp closed imaps
995/tcp closed pop3s
3389/tcp closed ms-wbt-server
5800/tcp closed vnc-http
5900/tcp closed vnc
6129/tcp closed unknown
MAC Address: DC:A6:32:69:49:xx (Raspberry Pi Trading)
Nmap done: 1 IP address (1 host up) scanned in 4.74 seconds
from: https://wiki.onap.org/display/DW/Nmap
Filtered means that a firewall, filter, or other network obstacle is blocking the port so that Nmap cannot tell whether it is open or closed.
Clearly layers 1-3 are fine so not an issue with the network itself – spent too much time troubleshooting this already. Think I’ll flash again & see if something is different.