I'm trying to enable the AOS graphs in my core 96.7, for it i put "UOFeatureEnable=0x20" in the servspecopt.cfg and add SendPacket(who, "B9801B"); in the login script.
The problem is when i create a npc a put some graph of AOS sometimes appear and other times not. If the graph appears when I attack the npc and this realizes the hit animation disappears and appear after the hit. =S

Any idea?

Let me guess: That happens on LBR npc's like e.g. fireant worker, meer mage ...

I think that was cause EA used different anim slots on these or didn't draw all the anims like before.

You can solve that by equipping those "blinking" npcs with a weapon, e.g.
Because i did that a few years ago, i don't know if there is perhaps an easier solution nowadays

You can use the [AttackAnimation (int animation ID {default 0 (wrestling)})]
entry in npcdesc.cfg to specify an attackanimation, and I dont remember how it was with the Damaged animations and LBR monsters, but I fixed that by adding DamagedAnim <int animation ID> to npcdesc and have my combat script to read that before it performs the animations.

I dont know how that is done in the core / distro combat systems, because Im using neither of them, Im having the combat hook return 1 and my own code control the whole combat, so someone who knows should tell more about the problem with damaged anims for npc's.