Teams doesn't recognise my users face

So I'm asking on behalf of one of my team members. We've recently started using Teams as our in-house communications platform, and of course everyone has discovered the background images feature. Mostly good times, and it certainly makes working from home more interesting for everyone.

One user however has been using these effects with no issue previously but has today reported that the background effect is the only thing his video feed displays. This has been verified to be the case from a call to me just a few minutes ago. He is within frame and the lighting should be sufficient but his video feed is only showing his background effect, he doesn't appear at all. Does anyone have any ideas on why this could be? Is there a sensitivity slider hidden away somewhere that's causing this? I'd prefer to sort this so he is still able to use the effects if possible.