If more than one type of hat is selected in the skills menu for one duplicant, the duplicant cycles through the animation as many times as a hat was selected but without any corresponding hat. When opening the skills menu again, no hat is assigned to the duplicant.
This mostly comes up when misclick, like giving a farmer the Farming hat, when I meant Crop Tending 1. If I let the animations cycle through, then open the skills menu to assign them again, it works fine.
Steps to Reproduce
Open Skills menu, on a duplicant with two or more mastered skills select each available hat, close the menu. After duplicant finished the hat animations, no hat is assigned.
This issue has not been confirmed by a developer yet.