Only reporting this because traders generate in larger worlds fine.
So this issue exists in multiplayer and in single player a20.6 b9. Only tested it on 3k worlds so far. The gist of it is that traders are not generated when using the Advanced Random Generation to make a world smaller that the standard 4k or 6k map.
First noticed yesterday around 1 PM EST when playing with friends. My computer is...mediocre at best, so the larger world sizes used to lag for me when connected via wifi with my old 8 GB RAM stick. I recently got Ethernet capabilities as well as a 16 GB stick, so me and my friends came back to 7 days to see how it runs now. To ensure I get as good an experience as possible, we decided to start small, with a 3k world. All three of us got NO TRADER for our "locate trader" quest. OK, no biggy, maybe it's a world corruption. We'll make a new one. This time, server host got a trader, but the other two of us got NO TRADER again. Going to the trader and speaking with them did not resolve the quest. I just generated a new world for singleplayer, played up to that point of the tutorial...and got NO TRADER again.
I decided to test a theory and looked for traders in the POI teleporter...and they don't exist. I don't know if the one instance of the trader existing was the only trader on the map or not, as we didn't continue playing much further. Oddly enough, this issue isn't present in mods such as Darkness Falls (only relevant due to lack of bug).
As I stated at the top: in 6k+ worlds (as far as I can tell) traders generate 100% of the time and I've not had this error, mind you I've only made 30ish games with 6k random gen worlds, but still.
Screenshot, showing both the quest and the POI teleporter with no traders listed. https://ibb.co/GP1Y1cC
Output log: https://pastebin.com/8gxUpzns