Stopsvalinn Didn't Drop

Discovered a village, went one zone from the village proper to explore outskirts. I got a message saying I found the Snapjaw that Wields Stopsvalinn. I saw a Snapjaw Spearfiend (NOT a legendary named NPC). Dispatched the snapjaw but Stopsvalinn was not amongst the items dropped.

My guess is that villager NPCs that happen to be any Snapjaw variants are eligible to be the "snapjaw that wields stopsvalinn" and the villager code conflicted causing Stopsvalinn to not spawn?