Not sure if it is a bug, haven't really got far into this game yet. But i proceeded to insult another captain, unfortunately did not get the name.. (maybe a noteworthy character) on the pirate settlement on cuba inside the local tavern. (I saved after the duel and not before)

The gold after winning this duel amounted to just over 1,000,000,000 gold.

Now i only had around 200k saved from trading goods. But this seems like an awful amount of gold from a single duel. 

Maybe this is balanced? In tune with a expense of owning multiple ships? Etc or the quests etc that go along with this mod. But at the moment not got the experience of playing through this game with these mods yet; any feedback appreciated :)

Thanks!

Edit: i duelled another captain just to test this out again, this time in cuba, havana. And not puerto principe; the reward was substantial, 66k but not anywhere close to the previous duel.

Edit 2: might just be me, but since duelling these captains.. i seem to have lost my ships, all 3 of em. I go to port and it says it is on the oyher side of the island, go to puerto principe port.. not there, and i am sure i have been to every shore line on top of that.. and nothing.. 😂

Edit 3: scratch that last edit.. i got back to where i was supposed to be... eventually.. clearly was in havana.. then went to puerto principe.. and had to go back to santiago.. 🥺 but yeah still no idea how i got 1m gold from that duel. :)

There is no random loot for dueling.  The other NPC captains that you can either insult, join for missions, are the same group of characters that you can select when you start a new game.  If you don't select them to play yourself, they are still out in the Caribbean, taking "missions" themselves, and show up in various ports during their travels, giving opportunity to either team up, or as you discovered, simply dispatch in a duel.  If you read the short bio for the characters, some are famous and notable, and others are not.  Their starting gold, weapons and ships typically match their "success" level and is noted in their character descriptions.  The loot you saw when you killed them, is the same loot you would have started with as that particular character, so it is not a random prize for the duel itself.  Some of them were very famous historical figures, so they would have been wealthy from the start during this time period.  For a few examples from the ERAS bios:

Henry Avery took the greatest single prize in history & he was never caught. Dubbed as the "Arch Pirate" & "King of Pirates"...

Gold: 600,000 Pieces of Eight
Equipment: Excellent equipment and very valuable items
Ship: Captured Mughul of India's treasure ship 74gun man-o-war "Ganj-i-sawai"
Level: 14

 Michiel de Ruyter is one of the greatest commanders of history...

Gold: 80,000 Pieces of Eight
Equipment: Good blade and valuable items
Ship: 92gun Dutch 1st Rate Man-o-War/Flagship of Dutch Confederate Fleet "De Zeven Provincien"
Level: 16

Blas Miguel...is famous as being the lesser of the two Corsican brothers.

Gold: 3,000 Pieces of Eight
Equipment: Basic equipment only
Ship: 16gun Barque-Longue "Un-named"
Level: 1

So if you dueled Henry Avery, he would have had 600,000 on him, and some very expensive heirlooms and weapons.  Blas Miguel, would only have 3,000 and some generic pistol and sword, probably not much else.