Okay, this is weird.

Mod-related function uses RemoveAllItems(). Follower has 90 steel arrows (and obviously other stuff). Long story short, the mod function kept freezing the game.

I thought that it had to do with another problem I'd been having, but even compensating for it, freeze.

Then I tried the RemoveAllItems console command. Intriguingly, it froze.

So I took varying combinations of the follower's gear until I figured out that leaving them with 90 arrows crashed the game.

And somehow, 100 arrows doesn't cause crashes.

Why?