Can you upgrade to the GA release 8.9.3.60 and see if the behavior persists?
3cx does not support the 8.9.3.60
i checked the same behavior with the 8.9.3.60
i upgraded 10 Snom 765 but only one have this problem
Sorry 10 SNOM 760
Dear Wolfgang.
Could you try factory reset in this device?
Press # key while booting and press option 1
Regards
Wolfgang Koppmann
Snom 760 blf+pickup turns on speaker after upgrade to
snom760-SIP 8.9.3.57