To pipe in here, I'm getting exactly the same error after upgrading to 7.57.
http://airwolfthemes.com/ubbthreads/ubbthreads.php/topics/4478/1I've a long-running post (a list of people who've passed away) that is updated often and in the past week or so when I go to edit it, all the text disappears on opening the edit.
It had some Bold and Typesize formatting in it for every line, but that all disappears with it.
I've done very basic formatting now cos every time I go to edit it, boom! it's gone.
