Looks like there is an issue with processing monthly repeat schedules after upgrading for 7.1 SP2 to 7.5.
The items I've found that are so far affected are:
Maintenance Windows
Inventory Policies
Software Delivery Policies
To reproduce this, setup a repeating monthly schedule for a Friday in the 4th week of month.
As not every month has a Friday in the 4th week (if Sunday is the first day of the week), the schedule is invalidated and doesn't occur.
The WORST impact is Maintenance Windows. It invalidates the maintenance window!
7.5 HF1 requires and agent service restart for the maintenance window changes to take effect.
Other policies that run outside of the maintenance window, such as inventory collection, simply never run.
No errors in logs on either the client or server as far as I can tell at this time.
Will be logging this via support.