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?
20MB is the max size so it's probably an issue with file size rather than a timeout or something along those lines. It's interesting that our webserver didn't block the connection before adding it to pictrs.
If it works with a smaller image please let us know.