I have two water sensors:
one RF433 Sensor, entity of class a binary-sensor in HA
one Shelly Flood Sensor, entity of class sensor (by mqtt) in HA
both entities are in group “Wasser Sensoren”
If the binary-sensor is true, the group change state
but if the entity of class sensor is true, the group don’t change state
any hints whats wrong? 
That’s because a sensor can have any value and the group doesn’t know which value means on and whuch means off. The true from your sensor could also mean that it’s off, the group doesn’t know that. One possibility would be to create a template binary sensor that shows on or off based on the state of the sensor.
OK, got it, thanks 
with template binary sensor it works fine!
