Hi,
I had the same issue with the map screen not showing events that had been imported automatically from Facebook but the maps functioned in the events pages themselves.
We fixed the issue by looking at the venues and checking that all address information had been entered correctly. We found that if the state / province was missing or the address line contained multiple entries (house name and road name) the venue would not show on the events map.
Once these addresses had been updated all of the missing venues (and associated events) appeared on the events map page as expected.
I hope this helps.