I was briefed last evening by an Apple senior support agent that Photos has a fault that has appeared between Mojave and Catalina, and that fault is around named people.
Imagine a photo of "Little Billy", a composite photo like parents put together with his sweet little face every Christmas for the past 10 years. Same kid appears 10 times in the photo.
Little Billy was detected by prior instances of Photos under Mojave and prior OS versions, and his name was below each picture with a circle around his face
On upgrade to Catalina, after Photos has done whatever upgrades it does to the library, several instances of Little Billy's name are now labelled "unnamed"
Attempts to name them "Little Billy" again look as if they work, but move away from that picture and move back and the name reverts to Unnamed.
This is the known fault, and one I and Senior Support Agent have been battling for several days.
Apple are working on this fault. I am told the fix is likely to arrive 'silently' as some future software update.
It seems logical to add your weight to this by making informed support calls to Apple, calls that simply show them the importance of the issue, but that is probably inessential