Someone (A) running Windows 10 and Chrome version 85.0.4183.121 successfully connects to a Jitsi session with two other participants (B & C). B has video turned on and B & C can discuss together, sound works. C can see the video from B.
After A connects, the Chrome tab shows it is using video or microphone. B & C see A appear in the Jitsi session with ah green network indicator. A does not see B video and does not hear any sound. After a few seconds the indicator turns gray and shows the person does not have connectivity. Even after 10 minutes, the connection remains active but gray, as if something persisted the connection but was unable to convey video or sound.
It could be a firewall problem.