The best way to deal with the error is to delete version 8.5.0 and 8.5.1 and reinstall 8.4.0.
That a default “feature” breaks people’s site is ridiculous! It’s even more ridiculous that the onus is put on the customer, many who may not be technically inclined, to jump through hoop after hoop to fix the problem just to turn off a feature known to break people’s site.
And, no, your website’s tech support will not help you with this. They will tell you to uninstall the update and revert back to the last version known to work. That is 8.4.0