Life cocoon - aggro issue

[Deleted]

Hi all healers and tanks!
I'm tank (dk and dh) and I noticed a 'funny' thing with the life cocoon.

I was running antorus to help a tank friend to gear (he was 945 and I was 960). Everytime the monk healer(another friend of mine) used life cocoon on the lower geared co-tank the bosses turned on me, even if I was just auto-attack.
During skittish weeks, running M+(17-18) as dk with my monk healer friend, sometimes when he uses life coccon all mobs turns red and I have issue getting aggro back. Looking at Omen we didn't see aggro drop however. We experimented last night in M+17 and 3/5 times the mobs went loose when he used coccon (we did on purpose on large packs).
I only notice it during skittish weeks and when I raid with a lower geared pal as co-tank.

Anyone had the same experience?
Thanks!

[Saverem]

Life Cocoon doesn't have a threat modifier.