I lose hydra heads from the typhon’s Veil 4-piece even with shield pylon active. This does not happen if I have other shield mechanics ( like barrier blades) active. Squirts necklace stays up and I don’t see my health bar moving.
To reproduce, equip at least 4 pieces of typhon, skill hydra, and make sure you have no shields active (barrier blades, molten wildebeast, galvanizing ward passive, etc). Go into an echoing nightmare, take the shield pylon and put down hydras. get hit by monsters and see your hydra count go down. As contrast, equip a shield mechanic (such as spectral blade: barrier blades, keep swiping), and see that you now don’t lose hydra heads.
This may be an old bug, but it is normally a non-issue as you wouldn’t play typhon without other shields. But as you can play nightmares using only the shield pylon as defense, this bug becomes a big deal S26.