Do you have an older Cerbo from before early 2022, serial number up to HQ2207. Those devices don’t have proper working Bluetooth.
From the manual:
Note for Cerbo GX units built up to and including serial number HQ2207; The built-in Bluetooth connection is disabled when the internal CPU temperature exceeds 53 degrees C (influenced by load and/or ambient temperature). For reliable operation it is necessary to use a USB Bluetooth adapter. Devices manufactured later (HQ2208 and later) do not require an additional USB Bluetooth adapter.
Beta testers reported success with the TP Link UB500 during V3.60 development. I use the older UB400, now superseded.
It might be that reverting to the older firmware makes the bluetooth work again, but next time the ambient temperature rises it will fail again. Really the only solution to have Bluetooth reliable on Cerbo GX with serial numbers up to and including HQ2207 is to install a USB Bluetooth dongle.