Hydras not working on would-be fire immune monsters

i have fire sundered charm on my fire sorc but when i put my hydras on the would-be fire immunes (venom lords, from river of flame to chaos sanctuary path) it doesn’t do any damage to them!! i am sure this is a bug because the charm is suppose to wipe the immunity?

and ya, LOVE the sundered charms!!

(Oh and doesnt work on summon druid pets :frowning: like spirit wolves i thought it would work on the summon vine and spirit wolves)