upgrade failure 9.5.4 to 11.5.30

[add1]

After a year I tried upgrading my plesk again, from version 9.5.4 to the latest 11.5.30, this time using pleskbackup/pleskrestore and also migration manager.
The results are (again) very bad. Both methods do transfer the actual content, but my primary concern are email accounts.
After restoring a domain (pleskrestore), mail users don't have a checkbox "Access to the Control Panel" so this method is totally broken and unusable. By using migration manager, the mail users do have this checkbox (WHY THE DIFFERENCE?), but their role (Mail user) shows some unnecessary (and for some users confusing) options like Subscription / My Resources etc. when they log in to control panel. If I change user role to "Application user", everything is as expected - the user cannot see anything besides their mail account in control panel which is a correct behavior. But I'm sure you don't expect me to manually edit 3700 mail users? Also, it doesn't make sense that "Application user" works fine and "Mail user" doesn't? Don't you think that's a bit weird?
Also, there is a problem with Domain administrator - the migration manager does the transfer, but the user is not allowed to make or edit mailboxes?! OK, I can edit the role manually, but again, do you think it's a lot of fun changing 500 domain administrators manually? We really don't have time for this...
Why doesn't the migration manager work properly after all these years?

 

[add1]

OK, the Domain administrator actually works after completing the "business model transition", but after that, all mail users disappear!? The mailboxes are there (and they work), but under "Users" there is nothing. And it gets better - if I try adding a new user account, so one could actually login to control panel, I get the "User account already exists" error, which kinda makes sense, because the mailbox with the same name already exists (but cannot use the panel).