JBL Charge 3 shuts down when connecting bluetooth

Hello there,

starting today my Jbl Charge 3 (8 years old, never had any issues) stopped "accepting" Bluetooth connections. It just turns off the moment my phone (or any other bt device, I tried 3 different) says "connected". It still works fine with a cable connection (audio jack), but once I try to connect bt it always turns off. What I have tried so far:

\-AC connected/disconnected \-charged for several hours \-hard reset (play+volume + button) \-different devices \-searched several shady posts for anything related but couldn't find any helpful information

Is there any way to repair it? Maybe a firmware update (which I did around 2 years ago), via USB, as I can't use the app because you know - it needs a Bluetooth connection :/ Anyone had similar issues or has any idea on how I can get my box back to being useful? I would rather not open it all the way because that might damage the insulation. Thank you kindly!