Throwing my two cents into the hat, as well.
I had a similar situation. Snapshots would't be rotated out of retention, regardless of what I set on the retention setting (on a subset of VMs ie not all of the).. The thing that solved it for my, was to recreate the affected schedule.
Do note that this will mark the previous backups taken by that technically deleted schedule, as being abandoned/orphaned.
But after I did this, snapshots would be properly rotated as expected.
