I can confirm I have this issue as well but I cannot figure out how to reproduce.
Seemingly sometimes I open my project and select an object to open the art editor screen, the palette appears blank. If I click the swatches, the color still shows up in the picker. Selecting a palette from the list doesn't populate the swatches with color.
I also tried exiting my project and opening a new project, the same issue persisted. Restarting C3 seems to fix it.
I stupidly didn't take a video last time it happened but here's a screenshot. Will follow up here if I manage to reproduce consistently.