Try picking a single movie and diagnose from there.
Open it up and check if it loads. Mine can be slow to fetch new images, so give it a few seconds. Then try refreshing metadata for that single movie.
Fingers crossed that fixes it. Depending on where you have images stored, you may have lost them.
If it does fix it you can select the movie folder and then choose refresh metadata for all movies, but it will take a while.
That's good. Did you recently change the setting for where images are stored? From the data/config folder to next to the media, or vice versa. I did that a while back and had assumed it would migrate them, but it didn't.