It's nothing to do with contact list length, as I have only 31 contacts.
So, basically, we can rule out:
- Graphics card drivers
- Low resources
- Contact list length
- Allow List length
IMO, this only leaves:
- Messenger 6.2.0137 bug
- Incompatibility between Plus and Messenger 6.2.0137
Since it happens to users of Plus, I'm tempted to go for the latter.