I agree in most cases.
Keeping a crayfish with an ACF is a terrible idea.
Crayfish are highly predatory and get quite large. Your crayfish in all likelihood is causing your ACF terrible stress and is very capable of harming or killing your frog.
This breed of FW crayfish never gets bigger than 3 inches and is quite passive, only comes out to forage for scraps and shys away from Tetras.
These frogs are actually fairly intelligent and believe me he is well aware of when that crayfish comes out.. if he is hiding that is exactly why. Can you blame him?
Please for your frogs sake strongly consider moving him to a safe home..
He's the biggest predator in the tank. I cause him more stress than any resident in the tank, and the only thing I really do to him is try to offer him food with my fingers.