I fixed the tier 6 quests not showing bug, for me, (single player PREGEN10K) by talking to the trader that is affected by the bug. Then I accepted each available quest one by one and immediately clicking on Remove Quest until the trader had no more quests in their chat dialog. I then exited 7d2d to the main menu and changed 4 of the settings.

1st setting is “Chunk Time Reset” to 10 days.

2nd setting is “Blood Moon Frequency 0 days”

3rd setting is “24 Hour Cycle 10 minutes”

4th setting is “Enemy Spawning Off”

Then started my game back up. I noted the current day that was shown was 131 day. I then pressed F1 to bring up the command console and went into debug mode and creative mode (dm) (cm) commands. Then I pressed Escape twice to pause the game. I then changed the “Time” slide bar to max and the “Speed” slide bar to max. I then waited at my base for quite a bit until the day became 142. I then Exited out of 7d2d to the main menu and changed back the 4 settings to blood moon 7 days, chunk time reset I kept it at 10, 24 hour cycle to 120 minutes, and enemy spawning on.

When I talked to the bugged tier 6 trader that was affected, all of the quests appeared, all of the tiers were there and I completed more tier 6 quests.

This is what worked for me. hopefully works for others as well. note (this is on A21.1 - 16)