I can not play Kologarn after i bring him back in my hand

impossible to replay Kologarn after bringing him back in my hand

im not sure but i got a similar problem , do you remember how it happened ??

In my case if i remember correctly it was a Shaman
Epic · Spell · The Great Dark Beyond · Discover two 8-Cost minions to summon with Taunt and Elusive.
interaction , do you remember if nebula was involved ?