Cannot Import Marriage Event from RM8 GED

Using Personal Historian Essentials 3, I have exported a GED from RM When I import the GED into PH 3, the “Import Genealogy/Which Events Do You…” screen shows no checkbox to select the Marriage event. Many other events appear and seem to import fine. But no Marriage events or facts import into PH 3.
The Marriage Fact seems fine in RM 8 and importing the GED back into a fresh RM 8 file shows the Marriage Fact - so the GED seems OK.
Why won’t PH 3 import Marriage Facts/Events from an RM 8-produced GED?

I don’t know Personal Historian but the problem may be that Marriage is a Family Fact Type rather than an Individual Fact Type. Does PH3 import any other Family Facts that you may have used such as Residence or Census?