There were so many mail ins I think the plan was to not count them all unless needed by Biden to win.
mail-in ballots were effectively early ballot harvesting
WI, MI and PA all counted (and are still counting) mail-in ballots last. That is why they are behaving opposite of the 47 other states. Trump leads early, Biden comes from behind.
In other states, Biden broke out to an early lead due to all early votes dumping first. Trump came from behind with election day votes.
Sadly, the VAST majority of votes added today in WI, MI and PA will go to Biden. In PA, Philadelphia county should dump an absolute truckload of Biden votes at some point.
IMO, Biden will win WI, MI and PA and be POTUS.