3cx windows client disconnect (only 1 extension)

[jwronken]

Hi
we've around 160 extensions, all of them using the Windows webclient, 3CX 18.0 update3 self-hosted in a datacenter.
One user (extension 1915) experiences at least 3-4 times a day that during a call (internal or external) after a random amount he gots disconnected.

This is an example from the activity log:

***********
08/10/2022 11:34:40 AM - Leg L:6981.4[Extn:1907] is terminated: Cause: BYE from local
08/10/2022 11:34:40 AM - Leg L:6981.1[Extn:1915] is terminated: Cause: BYE from local
08/10/2022 11:32:38 AM - L:6981.4[Extn:1907] has joined to L:6981.1[Extn:1915]
08/10/2022 11:32:37 AM - Leg L:6981.3[Extn:1907] is terminated: Cause: 487 Request Terminated/INVITE from 127.0.0.1:5483
08/10/2022 11:32:37 AM - Leg L:6981.2[Extn:1907] is terminated: Cause: 487 Request Terminated/INVITE from 127.0.0.1:5063
08/10/2022 11:32:37 AM - Replacing Leg L:6981.3[Extn:1907]
08/10/2022 11:32:30 AM - [CM503025]: Call(C:6981): Calling T:Extn:1907@[Dev:sip:[email protected]:5063;rinstance=3ecb8edde0a42df2,Dev:sip:[email protected]:5483;rinstance=cce6196582b373e3] for L:6981.1[Extn:1915]
08/10/2022 11:32:30 AM - [CM503025]: Call(C:6981): Calling T:Extn:1907@[Dev:sip:[email protected]:5063;rinstance=3ecb8edde0a42df2,Dev:sip:[email protected]:5483;rinstance=cce6196582b373e3] for L:6981.1[Extn:1915]
08/10/2022 11:32:30 AM - [CM503004]: Call(C:6981): Route 1: from L:6981.1[Extn:1915] to T:Extn:1907@[Dev:sip:[email protected]:5063;rinstance=3ecb8edde0a42df2,Dev:sip:[email protected]:5483;rinstance=cce6196582b373e3]
08/10/2022 11:32:30 AM - [Flow] Call(C:6981): has built target endpoint: Extn:1907 for call from L:6981.1[Extn:1915]
08/10/2022 11:32:30 AM - [CM503010]: Call(C:6981): Making route(s) from Extn:1915 to <sip:[email protected]:5060/UDP>
08/10/2022 11:32:30 AM - [CM500002]: Call(C:6981): Info on incoming INVITE from Extn:1915:
Invite-IN Recv Req INVITE from 127.0.0.1:5063 tid=6f5d43731f0d3a7b Call-ID=bfnSukIhvd-g4VfHI1nCEw..:
INVITE sip:[email protected]:5060 SIP/2.0
Via: SIP/2.0/UDP 127.0.0.1:5063;branch=z9hG4bK-524287-1---6f5d43731f0d3a7b;rport=5063
Max-Forwards: 70
Contact: <sip:[email protected]:5063;rinstance=8ed049bfc6c9da4e>
To: <sip:[email protected]:5060>
From: "xxxxxxxx"<sip:[email protected]>;tag=01464e48
Call-ID: bfnSukIhvd-g4VfHI1nCEw..
CSeq: 2 INVITE
Subject:
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REGISTER, SUBSCRIBE, NOTIFY, REFER, INFO, MESSAGE
Content-Type: application/sdp
Proxy-Authorization: Digest username="qxxxxxx",realm="3CXPhoneSystem",nonce="414d535962f37b2e04:ff3282525a19309eec4ee34b30206bb9",uri="sip:[email protected]:5060",response="e6906f501d9f86c93ac76694d4fa115d",algorithm=MD5
Supported: replaces
User-Agent: 3CX WebRTC proxy
Content-Length: 652

v=0
o=3cxVCE 18446744072979451098 18446744071905552637 IN IP4 127.0.0.1
s=3cxVCE Audio Call
c=IN IP4 127.0.0.1
t=0 0
m=audio 8568 RTP/AVP 0 8 9 111 63 103 104 106 105 13 110 112 113 126
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:9 G722/8000
a=rtpmap:111 opus/48000/2
a=fmtp:111 minptime=10;useinbandfec=1
a=rtpmap:63 red/48000/2
a=fmtp:63 111/111
a=rtpmap:103 ISAC/16000
a=rtpmap:104 ISAC/32000
a=rtpmap:106 CN/32000
a=rtpmap:105 CN/16000
a=rtpmap:13 CN/8000
a=rtpmap:110 telephone-event/48000
a=rtpmap:112 telephone-event/32000
a=rtpmap:113 telephone-event/16000
a=rtpmap:126 telephone-event/8000
a=ptime:20
a=sendrecv
08/10/2022 11:32:30 AM - [CM503001]: Call(C:6981): Incoming call from Extn:1915 to <sip:[email protected]:5060>
***********

All other users in the same office have never any issues, firewall settings are the same on user's PC.
Any ideas what the BYE FROM LOCAL can have caused?

User is connected via LAN like all other users.

Update: same happens no matter if we use webclient or windows client

thanks
Jan