I’m having trouble copying the html for uploaded jpegs but PNGs work fine. The png workaround is easy enough, but I wanted to flag this.
Does it work if you rename the file extension to .jpg before uploading?
I had a similar bug, see here. In my case it turned out the “jpeg” was actually a heic, and that file format wasn’t handled properly, not even after renaming the file extension to jpg.
I’ll have to try this next time I go to upload something. For the time being, I found it easier just to open it in Glimpse and export as PNG, then upload.