Since you wrote that the issue is still present for you I tested this with Jitsi Meet today. And again I wasn’t able to reproduce this bug.
Since we get different results using different apps (Signal, Jitsi Meet vs. 3CX) this might be a bug in 3CX… Could you please test this with Jitsi Meet? The app is free software (available on F-Droid) and it should be really fast and easy. Just open the app on both FP2 and type in a conference name.