I use Pimatic for more than a year now and I am using the Mysensors plugin 0.8.21 for more than 4 weeks now.
I use a serial gateway based on a arduino nano and a NRF24 radio.

I have already several sensors running without troubles and it appear to be stable.

What I see from your information is that the serial gateway is communicating, but seems to recieve nothing from your sensors.

If you can see on the PI that your gateway is started up, then the PI is able to recieve the information.

I debugged my serial gateway using the
serial monitor in the Arduino ide. This is also the way to test your sensors. In the serial monitor you can see if they are connecting to the gateway and sending information.