When choosing any Period for a maintenance or audit, a start date which only allows a single instance to be scheduled in the same calendar will cause any subsequent maintenance to be created for the same month and day of the next year.
For example–
Start Date: 10-01
Frequency: 2
Period: Quarter
Choosing this start date only leaves three months left in 2020 instead of the four that are needed. The function will create a maintenance/audit on 2020-10-01 and 2021-10-01.
A minor suggestion on the Periods: You may want to rename “Semester” to “Semiannual”.