The actuator remains closed, does not allow the pin to move upwards anymore

Thank you for the idea. However, all drives are NC.

Then the RTR simply closes the circuit because it was probably permanently open and the room is currently too warm... when it cools down, it will work properly again

The room probably cooled down last night. Currently, the left half of the room, which has its own circuit, is warm, but the right side is ice cold.

I would measure with a multimeter whether the actuator is working properly, meaning whether there is current on the terminal. Or whether there is no current on it.

The actuator has pressed the PIN down, the blue edge at the top of the motor is not visible, current is not measurable.

Due to the fact that there are relatively many cables in the junction box and it is tight there, I connected the replaced actuator with a terminal block; could this possibly be the error and be decisive?