Could you please point what exactly trader is and a way to make it appear in the game? I've tried to execute "Trader arrival" incident via devmode multiple times, but all traders were normal.
The trigger in dev mode is a map incident "MFI_ReverseTradeRequest", which pops up an event that lets you "finance" their caravan, which then makes a trader appear a day or two later (who in turn should pay more for a certain type of goods, like food or raw materials).
I'm looking at the "More Faction Interaction" XML-files, because I couldn't see it in game anywhere, but as far as I understand (I'm not really a modder), MFI adds four "TraderKindDef"s (MFI_EmptyTrader_Apparel, MFI_EmptyTrader_PlantFoodRaw, MFI_EmptyTrader_Weapons, MFI_EmptyTrader_Medicine). I guess MFI is then filling the traders' inventories programmatically ("MoreFactionInteraction.StockGenerator_BuyCategory" in "stockGenerators").
That's as far as I can go. But don't worry too much about it. I wouldn't really use the MFI traders, even without the bug, because at the point at which I am with my colony I don't need any more silver anyway. But if it is your mod that is causing the issue (I can't guarantee that, but I don't think any of my other mods change traders), I still hope these two mods could be made compatible.