You're right, I was looking in the wrong place. I found it and deleted it after disabling all the extensions but mysqli server behaviors. It worked fine but when I re-enabled the other 3 extensions, the same error popped up:
—The DynamicSelectList script does not define the applyServerBehavior function.
I threw the new cached file again and it's now working. But I'm going to be keeping an eye on it for the next few hours.... thanks!