When reloading the game: It breaks the following mods:
Max Buy Button Restorer
Bulk Buy 50
Reload Game Button
Toggle Autosave
Save to File
EDIT: Ok, NO, it's breaking most of the mods when loading it, it's absurd. I don't get why it breaks them.

So this is what happens on my client with those mods, and Shimmer Pop.
https://clipchamp.com/watch/4PQDgPcuUbZ

This is one of the issues I'm having, apparently it just works for me... I really have nothing to base anything off of. Maybe the new version has internal conflicts with itself from v2.1, because I didn't sanitize the mod's config by version checking. Try deleting the mod metadata under the Check Mod Data button and reloading the game.

I just installed Shimmer Pop for the first time and it works just fine alongside a ton of other mods I have installed, including the list above (except for Toggle Autosave, I don't have that one).

First, as Best Dad said, click CCSE's Check Mod Data button and delete Shimmer Pop's data and then reload the game. (Shimmer Pop should really be sanitizing older data. The fact that it's not will cause problems for all users who have previously used the mod.) If that doesn't solve the issue, then disable all mods, re-enable CCSE and Shimmer Pop, and enable only one other mod at a time to see which one is at fault. If that doesn't point it out, then something else entirely is at play here.

Not sanitizing the previous version config was a blatant oversight I didn't think about until now. I can push a small update that implements version checking to see if it reduces or completely fixes the issue some users are having. Other than that potentially causing Cookie Clicker to throw a fit (invalid config data being parsed/checked/edited) I legitimately can't think of a reason why Shimmer Pop would act any different from other mods. I'll try and get v3.1 pushed today which will clear all users' config and from then on, each update will just set the previous config on fire.

That seems a little drastic. Each update should try to migrate the user config whenever possible.