Does the app for the mini show the vertical rotating with camera pointing down (up would be OK)
In Go4 for mavic 2 and others it is shown on it's side, never tested if that actually matters but it's at odds with how most do it.
Make sure nothing metallic or worse magnetic is anywhere nearby.

To be honest it's a somewhat concerning fault, if the compass info doesn't agree with other data it is getting things can go bad quickly.
It could be worth contacting them for possibe replacement.