How about this ... anything I say in this thread is a guess!
Questions asked go unanswered so dunno if moving forward at all.
Will give one piece of advice ... don't hack core code!
"we have the missing parameter for the guest login."
still an issue, but now another is added ... auto backups not working ...
PHP Warning: filetype():Lstat failed for /data2/moodle/temp/backup//info_from_mbz_1582816764_FbpI
So have you looked at line 6796 in lib/moodlelib.php. Do so ... clue might be in there.
Have you tried Googling for "PHP Warning: filetype():Lstat failed"?
In that line see the 'double slash' right after backup and before info_from_mbz_blah? What's it doing in there? Do you have missing '/''s in your config.php file for path to moodledata?
In the debug see a reference to 'videoeasy' ... a plugin.
Is plugin compat with version of Moodle running?
Do have another suggestion ... turn off autobackups for now.
Find the course it was trying to backup and see if you can back it up from the course admin menu.
Me thinks if you continue down this path of not fixing issues ... another pops up ... not fixing the new ones ... and so on and so forth, eventually you will have so many 'pending' or 'plan to' fixes no one will be able to help.
No sense in even asking! :|