The 1.17.1 version is not compatible with Geckolib 3.0.13 and staying on an earlier version of Geckolib is not an option because that breaks other mods that depend on the newest version of Geckolib.

I am seeing no issues with 3.0.13 - can you specify what the issue is or post a crashlog. Thanks

https://pastebin.com/BEpskUYz

This same set of errors kept repeating.

Can you post your modlist. At first glance, the error does not seem to be due to a geckolib class

To help narrow the problem down, I created a separate clean instance with:
BOMD 1.2.1
Cardinal Components API 3.0.0
Cloth config 5.0.37
Fabric api 0.39.2
Fabric language kotlin 1.6.4 + kotlin 1.5.30
Geckolib fabric 1.17 - 3.0.13

It also happens with every instance of Geckolib for 1.17.1 past 3.0.10 including the new one that dropped today. That's why I suspect it's something to do with Geckolib because it's loading fine with Geckolib 3.0.10.

Edit: I just realized that BOMD itself was out of date. Surely enough, using the latest version seems to have fixed it. For some reason there was a brief time Curseforge wasn't notifying me of mod updates.