Hello Again!
I was testing the mod in my modpack and started a new world. Picked up a rock, got an achievement, game crashed. Restarted the world, picked up a flower (which triggered another achievement) and the game crashed again. It did not happen with Vanilla achievements.
https://pastebin.com/iYuuT0sC
The error seems generic, so I can't really pinpoint it anywhere. Testing it in a more compact environment (Botania+Qwertech [which adds a sound when an achievement is gained] + SSM-L) did not crash the game unfortunately, so my initial hunch wasn't correct.

Adding any other audio mods you had (e.g. MAtmos, Sound Filters) to the test instance might help reproduce it.

I made a temporary workaround for this bug until the true cause is found, it might lead to some temporary audio bugs when the crash is suppressed.
The sources are available in the weird-crash-workaround branch, and a usable jar is available here, or on the curseforge page as an alpha release.
I am going to be busy for a couple weeks, i will look into this issue more after i return.

Update:
I did try testing with all the sound mods installed and still couldn't reproduce it. On top of that, I seem to have recently managed to get the crash without the mod for the first time, after a couple hours of playing (again on an achievement) so I think it's safe to close this.
Thanks for your time as always, and feel free to reopen this in the future in case something else comes up.