It is possible to get error for front page if site is upgraded to 4.0. Unfortunately I don't have exact steps to reproduce - it depends on data - activities setup I assume. But when you logged in as admin, switch to 4.0 branch from 3.11 and reload front page you might end up with

Notice: Undefined property: stdClass::$completionpassgrade in /Users/stronk7/git_moodle/integration/course/lib.php on line 464

After running upgrade (view going to admin/index.php or cli) the error goes away. So it seems that the front page is trying to access to stuff that still not exists. Best course of action seems to update is_major_upgrade_required since 52206 introduced big db changes for modules