Following are the observed problem when making calls between two Jitsi cleints (version 2.11.5594 - actually the problem already exist in earlier releases). The problem starts to appear after making few repeated calls between the two clients.
a. Initial a call (audio or video) from from one jitsi client (sender-ubuntu) to another jitsi client (receiver-windows). Sender screen shows "Connecting".
b. The receiver client starts ringing and "Ringing" status is reflected on sender screen.
c. Click receiver phone button to accept call.
d. Receiver shows "Incoming call" but sender continue to show "Ringing"
e. Click receiver hang up button to cancel call.
f. Sender screen show "Connected" immediately follows by "Disconnected"

Note: Debug log attached is for reference only to better understanding the observed problem.
aTalk-android client is used and replaced the sender so debug log can be captured as shown below:
From debug log, it is found that 'session-accept' is only sent after receiver hang up call.
Partial flow graph is setup but immediately terminated by 'session-terminate.

Note: aTalk does not have this problem.

======== debug log on aTalk =========

10-17 07:16:01.588 D/SMACK: SENT (0): ....
10-17 07:16:01.608 D/SMACK: RECV (0):
10-17 07:16:08.798 D/SMACK: RECV (0): ....
10-17 07:16:08.818 D/SMACK: SENT (0):
..............

10-17 07:16:10.498 D/SMACK: RECV (0):
10-17 07:16:10.528 D/SMACK: SENT (0):

Jitsi usr click accept call button, but no 'session-accept being sent

Jitsi usr click hang up call button

10-17 07:16:43.508 D/SMACK: RECV (0):

Partial call setup but immediately terminated by 'session terminated'

10-17 07:16:43.608 D/SMACK: SENT (0):
10-17 07:16:43.828 D/αTalk: [20] org.atalk.impl.neomedia.device.MediaDeviceSession.log() Set format rtpmap:-1 opus/48000/2 fmtp:ptime=20;usedtx=1 on AudioMediaDeviceSession 674467378
10-17 07:16:10.548 V/Vibrator: Called cancel() API - PUID: 10479, PackageName: org.atalk.android
10-17 07:16:12.158 I/αTalk: [25] org.ice4j.ice.Agent.log() ICE state changed from Completed to Terminated. Local ufrag dcr2u1bsjnhkdp

10-17 07:16:44.618 D/αTalk: [29] net.sf.fmj.media.Log.comment() Here's the completed flow graph:
......
10-17 07:16:44.628 D/αTalk: [29] net.sf.fmj.media.Log.profile() Profile: graph building: 74 ms

10-17 07:16:44.668 D/SMACK: RECV (0):