PC [Modded] moonlord wont die

[Skeletundra]

Hey can someone tell me why my moon lord wont die. Im doing more than enough damage and its letting me get the eyes but when the core opens it takes 2 damage than replenishes back to full even when hes not doing anything that would cause him to heal
Please help

These are the mods

Bismuth
Elements awoken
Calamity
Base mod
Varia
Recipe browser
Malicious
Crystilium
Flight left timer
Thorium