Certainly this bike with 12 speed Di2 should be new enough that the bike shop will still be more than willing to check it out for you. Maybe even for free.

If it were a 3 year old bike, I might go to more lengths to solve on my own.

Welcome to BF.


Crap, the mistake in the title had me thinking this was new 12 speed Di2. Coming back later I see the OP said 9100 series. So if I didn't make another mistake, that's 11 speed.

Still if the bike is less than 2 years old, take it back to the shop. And I haven't met a bike mechanic in a shop yet that would not talk my head off about what does what and how to fix it when I go in and just ask simple questions to start a conversation.