Yeah, same thing happening to me as well.
Managed to get a longer game session by disabling the Ubi in-game overlay, but eventually game still crashes.
Running i9-9900k, 64gb ram, RTX 2080 Ti
Crash maybe caused because I have Windows 11, but I've seen people reporting it on Windows 10 as well.

@ubi-baron Apparently this is indeed a bug as they are not spawning in any of the locations which has flatfish around. I've managed to find regular and small size, but not big ones. I've managed to find other types of big fish with no problem.
Also, it seems that I'm not the only one who has this issue.

For me the bear is stuck inside cave ceiling and I cant interact at all after talking to Bjorn.
https://ibb.co/gF5W5Lt: (https://ibb.co/gF5W5Lt)

I have the same bug and as well with Gran Premio signs which show exclamation mark <!>
I think the issue is that when quitting the game, the game does not save world status, such as the map areas I've explored before becomes unexplored again (although the collectibles, chests and such stay collected).
I discovered that just prior of quitting the game you have to fast travel for the world status to save.
Game is quite bugged and needs a patch ASAP

Got my game working as it should, no crashes.. nothing! Reset my Nvidia 3D settings to default and voila, played game straight 3 hours before I had to quit for beauty sleep!

For me it seems the issue got fixed with new Nvidia driver.
Nope... still got crash to desktop, but at least now I got 2 hours of gameplay

Yeah, same thing happening to me as well.
Managed to get a longer game session by disabling the Ubi in-game overlay, but eventually game still crashes.
Running i9-9900k, 64gb ram, RTX 2080 Ti
Crash maybe caused because I have Windows 11, but I've seen people reporting it on Windows 10 as well.

@ubi-baron Apparently this is indeed a bug as they are not spawning in any of the locations which has flatfish around. I've managed to find regular and small size, but not big ones. I've managed to find other types of big fish with no problem.
Also, it seems that I'm not the only one who has this issue.

For me the bear is stuck inside cave ceiling and I cant interact at all after talking to Bjorn.
https://ibb.co/gF5W5Lt: (https://ibb.co/gF5W5Lt)

Njal seems to be stuck above the cave ceiling and no way to interact after getting to the point where I have to follow.
https://ibb.co/gF5W5Lt: (https://ibb.co/gF5W5Lt)