Question Importing project hangs on 2021.2.4f1

I have a bit large project (300k files in the Git repo) which we've so far kept on 2021.1.25 to avoid last-minute problems with shipping.

Now that it's shipped, I've tried importing it into 2021.2.4f1, and there are two problems so far:

#1: Some errors compiling the arkit plugin - which is strange because I'm importing the project for the Android platform: https://imgur.com/a/ISWlKuR

#2: The import process simply hangs. Last night I've started the import and this morning I found it hanging on an mp3 asset (at least that's what's been shown in the "Importing" dialog). I've killed the Unity Editor process after 14 hours of import and restarted it, now it hangs without any asset name being shown.

Any ideas how to even start debugging this?