Duplicants don't want to build until priority is set above 5

Hi

Another problem on my game.

It's a quite "old" game, because I play slowly and not very often. And during last months I was focus on build the next base.

But when I came back to the main base to build a new room ... well, My duplicants refuse to work on new build orders, even if my specialized duplicant for building is in the base, and even if they idle ... -_-

As you can see below, there's no duplicants set for the available errand.

Material is available and the path is clear.

In order to start building new things, I have to set the priority to at least 6. -_-

More strange, this issue only occurs on my main base.

L'Antre des Carnivores IV.sav