Thanks Sanjeev I added some screenshots of the All in One Video Gallery (AIOVG) and Schema & Structured Data for WP & AMP (SASWP).
Nothing was changed in settings. Worked before. Maybe Google made their data more strict?
Maybe if there is some way to add that thumbnailUrl field (extra; on top of the image file that is already in the schema), it will work? But how to do that?