Black blurred frame AFTER conversion

Dear Team,

I was in a breakout room, recording the meeting with different Zoom users (let's call them "guests"), which I let in the room two devices at a time. Once the meeting was over, I converted the video.

When looking at the video all the other guests' videos look alright, except for one, that has a black blurred frame all around themselves (I'd attach a picture but I don't find the upload button??).

Thing is: they looked alright DURING the meeting, no filters were on. 

Has this ever happen to anyone else?
Since during the recording I saw them fine, would it be possible to re-convert the file in a way for it to NOT have that blurred frame?

Hope it makes sense, otherwise just let me explain again.

Thank you for your help,
EAS