Over the years adding pics has proven troublesome.
I can add, at most, one pic using the attachments button. Subsequent pics I add by modifying the post and adding more pics. You see most of my picture posts have the "post modified at [timestamp]" at the bottom.
If I try and add 2 or more pics the session hangs and I get a white screen. If I do a "browser back" chances are poor anything got posted at all.
Today, even adding one failed. So I posted the text and go in and add the pics using the "Modify" feature. Judging by your time stamp you must have read the text between the post and modify.