I know there already was a discussion about this

while I was working on my own addon (I wish to add an RS47 handguard that supports the GP-25 slot), I found out that the moment I activated the GP-25 slot, it also activated the custom slot
by default yes, the AK-103 and AK-104 do have the custom slot, however, some handguards for some reason remove it; I suspect it might have to do something with the "ATT.ActivateElements = {"nogp34"}" argument in the code? the handguards that do this are:
Aggressor, Aspid, B-30+B-31S, CMRD, Hexagon AK, RS47, X47, WASR, all magpul handguards, UFM (on the VDM CS gas block option)
additionally, these gas block options also contribute to the same issue:
PPSHAK, TROY FLR, VS Combo

this issue is there with just ARC9, EFT Shared and Assault Rifles pack active and nothing else active