In short, if the blow hits more than one monster, then the activation of the ring practically does not occur. Counting the five necessary hits goes for each monster, but because of the basic 5% chance of crit, it is very easy to reset.
Isn’t a bug. The native 5% chance your toon has Vs a follower at 0% and a decent attack speed means it will hardly proc. Sadly some silly choices have been made over the years to nerf certain things only for the same net effect to be reintroduced later.
Put the ring on a follower with no other CHC rolls and something like Solanium and will see way more globes than you will get with it even though they nerfed the ICD on Solanium.