Server:
[INFO] .... [STDERR/]: [de.maxhenkel.voicechat.voice.server.Server$ProcessThread:run:192]: java.util.ConcurrentModificationException

[INFO] .... [STDERR/]: [de.maxhenkel.voicechat.voice.server.Server$ProcessThread:run:192]: at java.util.HashMap$HashIterator.nextNode(HashMap.java:1445)

[INFO] .... [STDERR/]: [de.maxhenkel.voicechat.voice.server.Server$ProcessThread:run:192]: at java.util.HashMap$ValueIterator.next(HashMap.java:1474)

[INFO] .... [STDERR/]: [de.maxhenkel.voicechat.voice.server.Server$ProcessThread:run:192]: at de.maxhenkel.voicechat.voice.server.Server.keepAlive(Server.java:205)

[INFO] .... [STDERR/]: [de.maxhenkel.voicechat.voice.server.Server$ProcessThread:run:192]: at de.maxhenkel.voicechat.voice.server.Server.access$100(Server.java:18)

[INFO] .... [STDERR/]: [de.maxhenkel.voicechat.voice.server.Server$ProcessThread:run:192]: at de.maxhenkel.voicechat.voice.server.Server$ProcessThread.run(Server.java:113)

Latest log:
https://pastebin.com/6uHBr9HG

The situation here is that it's actually working for everyone, except for this player (Larisa123789)

latest.log
(Client side log)

This is already a known issue (#70)

It should be fixed with the latest version.
Please let me know if it works for you.

We are currently playing on 1.16.4

I will port this fix to 1.16.4 if I know it works. Please consider updating, since almost every 1.16.4 mod is compatible with 1.16.5

yep, Im just waiting for a stable version of forge for 1.16.5

The fix is now also out for 1.16.4