Why can’t I see the dr doing telehealth? I can use regular FaceTime and the telehealth visits used to work but not any longer. The screen is black

I get a link sent via Text to join the Dr in a telehealth visit. It worked for 10 visits but the last 5 have been a black screen. I can’t see the dr. I can see myself in the upper right corner but not the doc and he can’t see me. No audio, no visual. Fixes? I can use regular FaceTime with my family but not this telehealth link. The dr says I’m the only one with this issue. I’m stumped