Could play videos fine - now get error message

I’m only moderately tech-savvy so I need help. I installed Jellyfin on both my Lenovo laptop running the current version of Windows 10 and on my Moto G7 Power. I I added the media I wanted to play from a Seagate external drive and voila! I was in business casting both from my laptop or my Android when the external hd was attached. I was able to watch fine for a week. Suddenly I’m getting this message:
Playback Error
This client isn’t compatible with the media and the server isn’t sending a compatible media format.
Anybody know what’s up? And you can reply directly or answer via this thread.
Directly would be