Originally posted by magnificent moose:

There is a known bug where you cannot pick up a certain fish after you drop it on the ground. I think this is a different thing however, you are no longer supposed to be able to pick up fish that you have not caught using the fishing rod.

It's not in the patch notes. My guess is they broke picking up fish some how.

Fish also now can jump on land and flop around why wouldn't players beable to pick those up.

Based on talks in thier discord it's purely a bug when it comes to picking up fish caught with a rod or not.