It was an oversight on my part. The original STF game includes some extra images including weapons (e.g., weapon_sniper_adv). I thought I could reuse them straightforwardly enough, however, the animation files for the weapons don't exist. So they will show up outside of combat, but in combat, they aren't present. I had used the unused weapon_sniper_adv for the heavy sniper variants, so all of those will be impacted. It's functional, but as you note the combat graphic is missing. If someone/me finishes out the animation files they would work, but I haven't been interested enough to work on it.

Seems the weapons work fine. Just the graphic of the weapon seems to be missing for some reason.

I have stumbled upon on graphical glitch. Tier 6 Shrike sniper and tier 7 Dragon sniper bought from specialty gear contact seem to have no visual when equiped in the gear tab. The guy just stands there with his hands holding nothing. Tier 7 Deadeye sniper bought from same contact shows up fine. I will test if the weapons still work fine in combat (soon tm) and edit this post with result.

That's correct. All of the new weapons are available via Contacts, Salvage, and Relics. However, all weapons have rebalanced.

Are the new weapons (minus the variant stubber) not included in the armories at all?