Here are my results from the last few days:
a) I factory reset an AP 3825i and synced it again
b) I changed the country code of another AP 3825i from Germany to Austria.
24 hours later the AP from a) and b) were still transmitting with more than 0 dBm.
Both solutions seem to work. So I had to facory reset about 26 APs, or take a another "Country Code".
I was not realy amused about both slolutions. Should I take cholera or black death?
I decided to have a look for a newer version and I found version 10.41.11.0009.
I installed the version on Saturday 11/17/2018 at 5pm.
And now 36 hours later still all APs are tranmitting power with more than 0 dBm.
Some background information: One week ago we made the version upgrade from 09.21.18.0009 to 10.31.10.0001 to 10.41.10.0014. Now with version 10.41.11.0009 everything seems to be fine.
Not clear what realy caused the problem, maybe the upgrade form 09.21 to 10.31. Now that's something for the experts. :-)