Modbus queueing requests

My HA has been in productive use for quite some time and is running 24/7. Modbus so far is purely experimental with all devices – three sensor units and one relay board – on my workbench. Last night on going to bed I turned off the sensor units. This morning they ignored the scan_interval and kept being read as fast and frequently as the bus allows. The relays were not accessible.
That looks as if requests were queued and now all those stored up during the night were executed first before anything new can be done. Not what I want. My plan is to call devices periodically, in practical use once per minute or less, and failed calls should just be thrown out and ignored after the timeout. How can that be achieved?
Another thing. In the developer tools reloading modbus.yaml does nothing, just a permanet blue ring, and restart->quick reload does not work for modbus. Only a full restart works. Is that normal with modbus? I’ll add my full setup.
Danke
Axel

#modbus:
- name: modbus_hub
  delay: 3
  message_wait_milliseconds: 100
  timeout: 2
  type: serial
  port: /dev/ttyUSB1
  method: rtu
  baudrate: 9600
  bytesize: 8
  parity: N
  stopbits: 1

  switches:
    - name: SW001
      unique_id: REL1
      slave: 1
      address: 0
      write_type: coil
    - name: SW002
      unique_id: REL2
      slave: 1
      address: 1
      write_type: coil
    - name: SW003
      unique_id: REL3
      slave: 1
      address: 2
      write_type: coil
    - name: SW004
      unique_id: REL4
      slave: 1
      address: 3
      write_type: coil
    - name: SW005
      unique_id: REL5
      slave: 1
      address: 4
      write_type: coil
    - name: SW006
      unique_id: REL6
      slave: 1
      address: 5
      write_type: coil
    - name: SW007
      unique_id: REL7
      slave: 1
      address: 6
      write_type: coil
    - name: SW008
      unique_id: REL8
      slave: 1
      address: 7
      write_type: coil

  sensors:
    - name: T01
      unique_id: t01t
      scan_interval: 15
      slave: 201
      address: 0
      data_type: int16
      device_class: temperature
      input_type: holding
      state_class: measurement
      scale: 0.1
      offset: 0
      precision: 1
      unit_of_measurement: "°C"
    - name: T03
      unique_id: t03t
      scan_interval: 15
      slave: 203
      address: 0
      data_type: int16
      device_class: temperature
      input_type: holding
      state_class: measurement
      scale: 0.1
      offset: 0
      precision: 1
      unit_of_measurement: "°C"

    - name: r0t
      unique_id: r0t
      scan_interval: 10
      slave: 180
      address: 11
      data_type: uint16
      device_class: temperature
      input_type: holding
      state_class: measurement
      scale: 0.1
      offset: -100
      precision: 1
      unit_of_measurement: "°C"
    - name: r0dt
      unique_id: r0dt
      scan_interval: 10
      slave: 180
      address: 12
      data_type: uint16
      input_type: holding
      state_class: measurement
    - name: r0h
      unique_id: r0h
      scan_interval: 10
      slave: 180
      address: 13
      data_type: uint16
      device_class: humidity
      input_type: holding
      state_class: measurement
      scale: 0.1
      offset: 0
      precision: 1
      unit_of_measurement: "%"
    - name: r0dh
      unique_id: r0dh
      scan_interval: 10
      slave: 180
      address: 14
      data_type: uint16
      input_type: holding
      state_class: measurement
    - name: r0tst
      unique_id: r0tst
      scan_interval: 10
      slave: 180
      address: 15
      data_type: uint16
      input_type: holding
      state_class: measurement
# define REG_LED 21
# define REG_STMP 22