Despite hall if fame showing >$500M net worth for over a day, the Moneybags achievement seems to be stuck at 497M and doesn't trigger.

The bug seems to be an order of operations issue. It is calculating NW for achievements *before* it calculates the updated NW. You can tell this because the achievement NW listed is the prior days HoF NW value.

There was a bug with a database change that caused the reset not to happen that day. Diablo triggered it for the likes of refills etc but the stats/nw scripts don't get run until the following day so it should be correctly updated now.