If you try to change the words of a comment via comment.php?action=editcomment It will occur in the message: critical site failure. This is needed when you change some spelling mistakes or sentences. If you also upload a file, it works. Looks like ‘add file’ is a necessary field for editing comments?
I just found out that if you click on fast edit, you can change and save a comment. So this could be a work-around for now. But for a full edit of the comment I need to work with a working comment.php?action=editcomment functionality.
Another question that I have is about edit a comment if you only want to delete a file. Is that possible somehow now? Or do I just delete it via FTP access? Unfortunately the WordPress user does not have FTP access.