An update: I finally went to Vinland and, as I expected, enemies are able to see me again just fine. Can't say for sure if they'd see me if I traveled back to England yet, of course, but I am not running into the bug in Vinland.

So the problem itself is that no matter what I'm doing, none of the enemies are noticing Eivor. I've done raids and stealth assassinated every single enemy at the monestary, did the weekly assassination quest, fought wolves, and even took out an order member...all without being spotted. I thought closing out and opening the game back up had fixed it, as some minor enemies from a mystery saw me, but another clash with an order member that didn't fight back proved otherwise.

Now, I can imagine what's caused this glitch, so I can probably get the game to fix itself, but this still shouldn't have happened. So I figured I'd report it regardless. I think what's causing this is that I told Randvi I would pledge to Vinland...and then decided to go around and do other things first. I think the specific nature of having to leave all your weapons behind to go to Vinland may be what's caused this. I should note that I have not yet met with Nessa at the docks. I don't have any proof that this is what caused this glitch, of course, but I figure it's worth detailing in case my hunch is correct.