I have removed myself from the beta version. 100% of all calls yesterday I was not able to answer.
I have this same issue on Samsung S10+ with 3CX 16.4.0.111
The call comes up on locked screen and I see the popup to answer or reject the call. Pressing answer does not answer the call (nothing visible happens, no sound). After logging in to the Samsung, the 3CX app is displayed, the phone button is red, indicating a connection, but there is no connection, or at least no conversation. Pressing that red button seems to disconnect, the 3cx app disappears from focus.
I had no successful answered call.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.