1 prior coverage end date rule is not working as expected

Summary: For Promotion Life event, we have waiting period logic and coverage should start first of next month after waiting period ends. Coverage start date is working fine but previous coverage end date is not coming properly.

Content (required):

We have to plans Staff and Manager plan. Staff plans are applicable to hourly employees and Manager plan is for salaried. Now during promotion, there is 90 days waiting period in which employee will continue to be in staff plan till 90 days is completed and then his manager plan starts first of next month after that 90 days waiting period window. Below is the setup we have,