Hi! Thanks for asking [and sorry you are seeing this problem], but to answer the question first some background:
When Webex connects to each participant, Webex is continually testing available network/client facilities [particularly bandwidth, CPU, screen real-estate/layout chosen]
What this means is, when Webex interacts with your client and constructs the conference view of participants and sends them to you, it is making a decision based on your available facilities [particularly BW] when it sends the meeting participants/layout to you.
Now of course it is possible that user that does not show in the layout either has their camera off [you will see the 'video mute' icon in the participant list if this is true], or they could be using a 'physical' video mute such as a shutter/piece of tape [should look like they are sending video, but the view is of the physical obstruction, usually completely black if they are doing this], and lastly, if that participant themselves are connected at an extremely low bitrate such as <<400 kb/s, Webex will no longer transmit their 'send' from their video camera into the meeting and you will see their avatar instead. This is common for mobile participants.
Hope this helps so the reason is one of these three. Go into control hub/troubleshooting to find the participant in question to see if their connected bitrate into the meeting was low enough that this was the issue.
thank you,
~Joe
