I would be inclined to do Settings > System > Reset options > Reset mobile network settings.
Just tried that, unfortunately no dice still showing the incorrect IMEI numbers.
Like I wouldn’t even mind doing a factory reset, if the issue is fixed thereafter but reinstalling everything just to have the same issue doesn’t seem worth it and I doubt it would help with the IMEI codes.
EDIT #1: Related thread was opened for this problem specficially: Sim 1 Not allowed in e/os 3.1.2 ?!?