So I recently switched to a Samsung Galaxy A50 with One UI version 1.1 via Android version 9.
So I had a problem with thumbnail regeneration. The DCIM / .thumbnails folder deletes the contents the next day (which is presumably a function to save memory). However, the problem occurs when the content can not regenerate itself.
The gallery apps itslef works fine and regenerates the thumbs properly, but does not create new thumbs in the DCIM / .thumbnails folder, which I can not post on Instagram and Reddit.
I've tried deleting data and clearing the gallery cache, restarting my device, but it's still not good.