Well, I received some news from my local drone shop which sent the case directly to dji... Here's what dji replied about signal disruptions:
“Hello,
this is not a firmware issue.
During the update one of the parts was damaged and will have to be exchanged here.
If you absolutly want to try a downgrade do this:
Start the complete system and connect to you device. Open the app.
In the white mainscreen, tap and hold the Academy button for at least 5 Seconds. The screen will turn black.
Then you can select and download a firmware (be sure to be connected to the internet) and install.
You can test it afterwards, but I do not believe it will solve the issue.
Best Regards,
Technical Support
DJI GmbH”