Shelly Dimmer 2 often "ignores" calls from homebridge-shelly
**Describe your problem**
I have a setup where the shelly dimmer should turn on and off (controlled by homebridge-shelly) triggered by automations from homebridge-calendar. Very often, the dimmer just does not turn on, despite necessary events being triggered.
I see that homebridge-calendar fires its events and also homebridge-shelly executes the calls to the dimmer and even logs a 200 status code which I hope indicates success. However, the dimmer does not react and stays turned off:

```
[22.11.2020, 07:00:00] [Calendar] Pushing calendar sensor 'Geckos' state 1 - value 1
[22.11.2020, 07:00:00] [Calendar] Pushing calendar sensor 'Lampe Terrarium Calendar' state 1 - value 1
2020-11-22T06:00:00.005Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] Sending HTTP event '10.19' with data: {"characteristics":[{"aid":10,"iid":19,"value":1}]}
[22.11.2020, 07:00:00] [Calendar] Scheduling next action in 43199994ms
2020-11-22T06:00:00.043Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] HTTP request: /characteristics?id=11.10,20.10,11.11
2020-11-22T06:00:00.043Z HAP-NodeJS:HAPServer [0E:32:12:20:FC:D3] HAP Request: GET /characteristics?id=11.10,20.10,11.11
2020-11-22T06:00:00.043Z HAP-NodeJS:Accessory [Homebridge FCD2] Getting value for Characteristic "On"
2020-11-22T06:00:00.044Z HAP-NodeJS:Accessory [Homebridge FCD2] Got Characteristic "On" value: false
2020-11-22T06:00:00.044Z HAP-NodeJS:Accessory [Homebridge FCD2] Getting value for Characteristic "On"
2020-11-22T06:00:00.044Z HAP-NodeJS:Accessory [Homebridge FCD2] Got Characteristic "On" value: false
2020-11-22T06:00:00.044Z HAP-NodeJS:Accessory [Homebridge FCD2] Getting value for Characteristic "Brightness"
2020-11-22T06:00:00.045Z HAP-NodeJS:Accessory [Homebridge FCD2] Got Characteristic "Brightness" value: 100
2020-11-22T06:00:00.046Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] HTTP Response is finished
2020-11-22T06:00:00.066Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] HTTP request: /characteristics
2020-11-22T06:00:00.066Z HAP-NodeJS:HAPServer [0E:32:12:20:FC:D3] HAP Request: PUT /characteristics
2020-11-22T06:00:00.067Z HAP-NodeJS:Accessory [Homebridge FCD2] Processing characteristic set: [{"aid":11,"iid":10,"value":1},{"aid":20,"iid":10,"value":true},{"aid":11,"iid":11,"value":100}]
2020-11-22T06:00:00.067Z HAP-NodeJS:Accessory [Homebridge FCD2] Setting Characteristic "On" to value 1
2020-11-22T06:00:00.068Z HAP-NodeJS:Accessory [Homebridge FCD2] Setting Characteristic "On" to value true
[22.11.2020, 07:00:00] [Terrarium Lampe eingeschaltet (Notification)] Send notification to IFTTT: Die Lampe im Terrarium wurde eingeschaltet.
2020-11-22T06:00:00.073Z HAP-NodeJS:Accessory [Homebridge FCD2] Setting Characteristic "Brightness" to value 100
2020-11-22T06:00:00.075Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] HTTP Response is finished

2020-11-22T06:00:00.171Z superagent GET 192.168.0.123/light/0?turn=on&brightness=100
2020-11-22T06:00:00.236Z superagent GET 192.168.0.123/light/0?turn=on&brightness=100 -> 200

2020-11-22T06:00:00.278Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] HTTP request: /characteristics
2020-11-22T06:00:00.279Z HAP-NodeJS:HAPServer [0E:32:12:20:FC:D3] HAP Request: PUT /characteristics
2020-11-22T06:00:00.279Z HAP-NodeJS:Accessory [Homebridge FCD2] Processing characteristic set: [{"aid":10,"iid":19,"ev":true}]
2020-11-22T06:00:00.279Z HAP-NodeJS:Accessory [Homebridge FCD2] Registering Characteristic "Contact Sensor State" for events
2020-11-22T06:00:00.280Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] HTTP Response is finished
...
2020-11-22T06:00:59.523Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] HTTP request: /characteristics?id=11.10
2020-11-22T06:00:59.523Z HAP-NodeJS:HAPServer [0E:32:12:20:FC:D3] HAP Request: GET /characteristics?id=11.10
2020-11-22T06:00:59.524Z HAP-NodeJS:Accessory [Homebridge FCD2] Getting value for Characteristic "On"
2020-11-22T06:00:59.524Z HAP-NodeJS:Accessory [Homebridge FCD2] Got Characteristic "On" value: false
2020-11-22T06:00:59.525Z HAP-NodeJS:EventedHTTPServer [::ffff:192.168.0.108] HTTP Response is finished
```
When I manually turn on and off the dimmer via Home-App, it always works.

**Describe what you have tried so far**
I moved the homebridge to a more powerful rapberry pi and connected it via ethernet instead of WLAN but there was no improvement.
Since I see all the events in the homebrige log, it might be an issue on the shelly device itself. Are there any known issues that might be responsible for this behavior?

**Environment:**
 - Shelly device(s): Shelly Dimmer 2, Firmware: 20201124-092706/v1.9.0@57ac4ad8
 - Plugin version: 0.15.7
 - Device running homebridge: Raspberry Pi 4
