When I am posting I notice after uploading a photo to post that there is 1 blank line before the photo attachment. I remove the blank line and then I add the content after the photo. This is the only common factor that I can think of.
This bug is not consistent, but it is persistent. Maybe 1 in 5 posts will remove 1/2, or more of my written content.
I am using brave browser with the nos2x extension on Linux.