There seems to be a lot of varying bugs with missing Traders but here is a solution for one of those bugs I encountered. I could enter the shop but there was no trader behind the counter. I restarted and same thing. Out of frustration i hit his counter with my stone axe but i actually got a "blood spatter" from that. So I did little jumps (cramped room) and I could just see the top of his head. He is still behind the counter but either his model has pancaked flat or he is mostly in the ground. Clicking on him during a micro jump still let me trade with him..
Hope it helps.
Hope it helps.