Word of warning:
Yesterday MitID got updated to version 3.0.2 (version code 75). Then the app got permanently stuck in the initial blue / logo screen. I was not able to get the app "unstuck" (force stop, rebooting phone, changing permissions). Note that there is no error, no "rooted" message, nothing — the app simply doesn't load.
I thought that something might have gone wrong with the data migration, so I tried revoking the authenticator, uninstalling the app, and installing it again. That didn't solve it. Whatever is wrong, has nothing to do with the data but a more general app issue.
I recommend that anybody who didn't update yet go to Play Store and disable automatic updates for this app. If you did update, just wait for a new update that might fix the app — uninstalling/wiping won't work and you will need to revoke and set it up again in the future.
I have another, non-GOS backup phone, in which I updated the MitID to this same version. It did not get stuck at the loading screen. I'm theorizing that MitID misbehaviour might be related to either some difference in GOS or being unable to cope with sandboxed Play Services with a reduced set of permissions. I only have granted Play Services the following permissions: Location, Network, Notifications and Sensors.
I used Aurora to manually download version 73 (3.0.1) — 74 was not available. That worked, and the app is not stuck at the loading screen. Whatever broke, it was due to a change in version 75.
Since I need to re-activate my authenticator now, I may try updating to 75 again and check if giving more permissions to Play Services changes anything.