Try this:
1 - disconnect the BP animation update in your animation BP (this means the event graph will do nothing)
2 - on the event overlaps, get your mesh → Get Anim Instance → cast to ZombieAnimation → set Can attack.
So basically, your actor BP will set directly the canAttack variable in your animation BP.
Something like this:
Don forget to disconnect the update event in the event graph in your animation BP.