[2021] PTS did not nerf Vampire’s/Thorn/etc, but there are bugs

In short, the fix they are testing and deploying seems related to multi-hit weapons triggering on-hit effects multiple times per attack.

On live:

An explosive splitter weapon can stack Tenderizer to 40%, Suppressor to 40%, Strangler Heart poison to 10+ stacks, Vampire’s to 10+ concurrent stacks, Gamma Wave burn to 10+ stacks, etc all in one blast. It can remove a Dodgy opponent’s AP bar in one attack. And so on and so forth.

On PTS:

Each of these effects only triggers once per attack, no matter how many projectiles land from the single attack.

Melee weapons and ranged weapon bash attacks (e.g. Minigun Shredder) are BUGGED and only trigger the healing once per enemy after the first time you hit the enemy. The workaround is to swap weapons between each attack in order to regain the Vampire effect, but obviously this is cumbersome. This bug is expected to affect the other on-hit effects such as those from Thorn armor, Tenderizer Perk, Talons mutation, etc.

Ranged weapons can continue Vampire’s healing after their first shot on the enemy, though a few may also bugged.

More details and testing on the PTS thread: https://bethesda.net/community/topic/448682/bug-vampire-s-legendary-effect-does-not-work