Do you also have image upload issues sometimes? I have posted a screenshot of how it looks when it fails. It is a known bug -> https://github.com/LemmyNet/lemmy-ui/issues/1489
Do you maybe know how to get around it, and still be able to upload the image?
Most of the time these errors are related to pictrs not responding fast enough. Usually because it has to convert the picture, video, gif and pictrs is already busy.
If you ever get these messages try again after 30 seconds (or so) and it should be fine