So after installing b4 I created a new database, set as active/default, and removed the old one.
Importing a few hand histories (cash, not tournament, only 350 or so hands total) into this DB via auto import did not show any players/stats until after PT3 was restarted.
Starting over with a fresh DB the same was seen with manual import.
Repeating again with an empty DB and using manual import on a mixture of tournament & cash histories resulted in the tournament players/stats/etc being seen under the tournament tab immediately as I would expect, but the cash players/stats werent present until after a restart. Its likely relevant that the tournament hands were all imported first, followed by all the cash hands (as a single import, this ordering was just a result of the filenames). Totals were around 3500 tournament hands, 350 cash (yes, the same hands as above).
Switching to a different active database and back again results in all players/stats being shown correctly without a restart being required.