Seems like Julia’s function passing behavior is tricky to catch and profile - the specialization solution is the same as this solution proposed in 2018, and folks in the thread noted that diagnosing this with @code_warntype can be tricky.
If these functions behave this way, what about for functions inherited by closure? I realized a lot of my code optimizations over the last week had to do with calling closure-inherited functions in a specific way to ensure specialization.