[SOLVED] Where do the random temperature values come from in the demo file and why do they keep popping up

Like many, I use the demo file as a basis for my own openhab configuration, but I am puzzled by something.
The Demo file as is, has items like these:
Number Temperature_GF_Corridor “Temperature [%.1f °C]” (Temperature, GF_Corridor)
Number Temperature_GF_Toilet “Temperature [%.1f °C]” (Temperature, GF_Toilet)
Number Temperature_GF_Living “Temperature [%.1f °C]” (Temperature, GF_Living)
That seem to give random values all in the 18-25 degree range that seem to come from nowhere.
Now if I add an mqtt channel like e.g.:

These random values are replaced by the input from my channel as they should… but I noticed that if I increase the time interval for updates (meaning it takes longer to receive a new mqtt message), suddenly those random values from the demo file pop up again.

As I thought that maybe somehow there is an input that I dont realize, I set up new temperature items that were initially not in the demo file, such as
Number Temperature_GF_Tuin_Coop "Temperature Coop [%.1f °C]" <temperature> (Temperature, Garden)
but these also get a random output like 22.3 degrees or in that range. I have no idea where those values come from or how I get rid of them so they do not pop up inbetween channel updates

Oops, I think I just discovered it in the ‘rules file’