So far, I've been able to reproduce a few transformations:

* www[0-9].example.tld -> [0-9].example.tld, e.g. www1.nyc.gov -> 1.nyc.gov

* example[ac|co|gov|edu].tld -> example.[ac|co|gov|edu].tld e.g. exampleac.uk -> example.ac.uk

My guess, as someone else further down the comments mentioned, is that some URL handling library is doing more than expected to its input. I filed an internal bug report referencing some of the public reports from a dev build of Android 12, so hopefully this will get triaged soon if someone hasn't already done a similar reproduction.

(I work at Google, but on nothing remotely related to Android.)