App Restrictions are a function of Jamf Pro and Jamf School. Its more or less something called Application Blacklisting, and its anything but random. Basically, your school's admin specifies a path or process name and scopes out the restriction and that thing is blocked on all devices within the scope.
If it appears inconsistent, its likely due to poor testing on your school's IT department and they did not flesh out the experience. My gut says the scope is bad.
The scope can make it appear random, for example if they have it scoped to a network segment then when you are not at that location the block won't apply but will suddenly apply when you are at that location. Say they wanted the block to apply when you are at school but not at home, that would be network segment dependent. All of this is check-in based and dependent on the Jamf Framework updating (not MDM profiles) so it is a bit delayed.
