@link31s - I'll be watching this with interest to see what response you get, but a point of clarity - the 2/28 app update was just a OW app update, not a firmware update (firmware is the software that's on-board the board itself).
I'm surprised to hear this could be happening, because in theory the OW app being updated should not be able to affect the board's performance at all (after all, you can ride the board without connecting to the app - that's because it's the firmware that actually "drives" the board, and the app is only used to interface with that to "see" it, and change certain adjustable parameters). But it sounds like you've experimentally validated your diagnosis. That's worrying.
Just FYI, the board behavior you are describing sounds very similar to a problem my friend has been having on his XR, pre-dating the 2/28 OW app update. He's getting ready to send his in for service, they suspect a bad cell.
Anyway, I appreciate you reporting this, and later today I'm going to try to go ride around and make sure my board still behaves same (I've ridden it once since the update but not past 50%).
One other complaint I'd like to make, is that the OW app did not give me any CHOICE but to update to the new app version on 2/28. I could not use the app unless I updated it (the update window could not be closed or opted-out of). I prefer not to make software updates right away for exactly this reason - I let the early adopters let me know if there's a problem, sometimes a software update is buggy and/or worse than the prior version.
Unless it's a critical safety/security update, it should never be forced on users, users should be able to opt-in or -out of updates.