After a total of 3+ hours trying to locate the source of an "unknown exception" from Mixins causing a crash, I have pinned it down to this mod (primarily by disabling everything except this mod). I do not know what exactly is causing it (thanks for that, Mixins), but I do know this appears to be specific to 1.20.2, version 1.1.17. If this can be replicated and is not some freak error causing me extraordinary trouble, it is of such severity as to make everything running on it unusable.

Could you post the crash log you are getting? I am not able to recreate this problem with Iceberg by itself.