Hum, had not realised that but am quite prepared o believe it! Interesting.
Gardena might be ‘special’ here because, as you say, its all to do with a cloud API that still “works” when your devices are absent. It’s going to be doing something like connecting to an account, and setting “child” status according to info from the account.
Disabling the ‘account’ Bridge thing might have lasting effect, but that’s no use to you?
An example managing Things involving 'parent ’ Bridges, its essentially OH2 but might give ideas-
Essentially it detects a ‘child’ Thing error, and sets the ‘parent’ Bridge offline. With automated retry later, which you may or may not want.