I have used this “behaviour” in several games; combining crayfishing in winter with wild food in summer and it has worked very well but in my present game it doesn’t work anymore. It’s some kind of bug and I’m sure it’s nothing you can do to fix it, Tom but I’ll tell you anyway.
When you have several gather’s huts (I first noticed it with 4 huts and 12 gatherers) and set several crayfish spots (about 10) it looks like the game can’t assign a certain gatherer to a certain crayfish spot anymore. After I saw that the spots wasn’t harvested after the winter, I watched a few gatherers a bit closer and they went from one spot to another doing one work and back to a hut to harvest one firewood then back to one crayfish spot, often far away. Not much was harvested.