Thumbnail videos during Presentations

[3640593868]

When sharing a presentation the thumbnail videos of participants (and myself) disappear. This only started yesterday. I have checked my settings. They are not set to "hide participants". Can anyone advise? The participants can still see each other and me. We can still all hear each other. 

[Lilydale]

I am experiencing the exact same issue starting yesterday as well. I would love to know how to remedy this!