[2022] Shattering Impact mod not working on the Vastilok and the Sarpa

Shattering Impact remove a specific amount of armor per hit, it's not proportionate. So you might have been seeing the effects of testing against a different type, or a different enemy level.  e.g. a level 100 Heavy Gunner will require a lot more hits to remove their armor than a level 10 Butcher.

(Also be careful if you're dealing with Heat damage since Heat also affects enemy armor value)