I have a location with a MICS 6.1 and CP100 ver 2.1 and routinely there are messages that are delivered late. For example they check the mailbox at noon and then at 4pm and there is a new message dated at 9am in the box. I have put all 4 ports into notification and then did a reboot. The problem subsided for a while and now it's back. I would definitely say its a problem and not user error/imagination.

This location has a PRI and rather active on phone calls and vm usage. Would a 150 be better suited? Does rebooting really help this issue?