[GAMEPLAY] Dragon doesn't fight back

I was playing co op as KhaZix and I went to do the earth dragon. I started attacking him as soon as he respawned and everything was normal then I used my ult twice (unempowered R) went invisible and after the second time he just coiled up and sat like it had reset but the hp bar did no change and i kep attcking and killing it shortly after. I have never seen this kind of animation of the dragon before, nor this kind of interaction with it, and this is the first time it happened to me ( I forgot to take a screen ) I did not try to recreate this occurance details : Buffs I had: Rift Herald, Gift of Heavy Hands - cant remember what else... but definitely not blue or red Items are the same as in the picture I was level 10 i think

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