Do your snapshots include the state of the memory?
Negative. We do not snap the memory or quiesce.
I'd start by comparing the virtual machine log files of "quick" VMs to "slow" VMs regarding snap creation and deletion.
Actually I think you were correct in your first post! Responsibility for snapshot for maintenance was handed over to a junior and after speaking with him have learned he HAS NOT removed the check mark for backing up system memory so I'm pretty sure this explains it.
Will make sure during next months cycle.