The OPs bike is a 2020 model, so I assume that it has very few miles on it. It is conceivable (but unlikely) that there is some crud or a metal burr in the grove that restricts the movement of the steel balls. To find out for sure, you would need to drop the motor out, split the cases, pull the transmission out and inspect the output shaft.<< snip >>
Getting back to the OP's issue, could there be an issue with 1 or more of the steel balls not moving far enough when the bike is moving, which would result in the bike blocking - or partially blocking and making difficult - the OP's attempt to upshift from 1st to 2nd?
I'd probably suggest that the OP (1) log the problem with his Dealer so that there is a record of the problem under warranty, then (2) change the oil, and (3) put a few more miles (say 5,000) on the clock. If it is still a problem than take it back to the Dealer.
As for his other problem of the engine dying when taking off up a hill,
** edit - as the 2020 models are "ride by wire", I really don't have any suggestion.