The Haunting shard will only build up stacks when the Abyss Lord uses his secondary attack rather than his primary. I assume the issue is because his primary is channeled since if you have full stacks when starting a primary attack, the ghosts will spawn.
This may be indicating that all channeled attacks can only activate a shard's effect once, at the start of the attack. Unless this bug is Abyss Lord specific.
I too have made a bg report but i included all the shards that i have that dont work on AbyssLord primary attack. Still under review will post the link on forums when its done.
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Nearly all Shards that affect primary attack are failing to work on Abysslord
Pumpkinator - Does not work.. interestingly enough this does work with Poison shield from Pet probable other pets aswell
Overwhelm - Works atleast before 19.5 havent tested since (i believe this is working have tested now)
Lightning Touch - No effect no increase in damage noticed
Drenching Strike - No effect - Enemies never appear Drenched also Tested with Lightning weapon no stuns ever happen..
Skeletal Bind - Never gain charges or cant use right attack to spend charges at least one of these is not working making the shard broken on Abyss Lord
Ravenhost - Partially works. Can Charge but doesnt automatically fire. need to stop attacking then attack again for it to work. unlike other classes when you can full auto attack
Burning Strike - No effect
Elemental Weapon effects also dont appear to work with Abyss Lord.
I can confirm this, nearly all "your primary attack..." shards do not work on abyss lord primary attacks by using his channeling. This includes lifeleech, anti air, haunting, and probably alot other.