A few things I've found:
1. Could this be the issue? https://moodle.org/mod/forum/discuss.php?d=365798
2. I found that I was able to recreate the error on my machine by spamming the save button when editing an online text assignment.
Re: Error on online text assignment "You have existing submission data. Please leave this page and try again."
by Tavis Bogue -
Number of replies: 0