Playing Blackwood single player. Just a little NE of Freeport island, 16.70 Long. 2.38 Lat. I tried jumping in the water to pick up a crate and I fell to the bottom and died. Happened 3 times trying to get my possessions back. I even tried Diving suit and still just fell underwater and died. I am in a new Brig first time out. Earlier in this game, a few days before, I wnet to top center arctic island in a Sloop. I was able to jump in several times, maybe 4 or 5, and recover crates. I am on a very similar voyage back to the same arctic island along very similar route, maybe a bit further east this time, not sure why I am dying this time, but worked when I was in my Sloop. I suppose the lesson here is to only jump in without any inventory to test first? I only lost a couple of pistols and my metal weapons and implements, but it would be nice to be able to get crates, or even fish, without just sinking or falling to the bottom and dying.
Update : So this would appear to be a localized issue. I moved a bit further NW to 35.71 Long. -15.92 Lat. and saw a dolphine swimming by the Brig and I stopped and jumped in and no death. Not sure what is up with that particular spot. I also restarted my game in the old spot with no effect.