Process bar disappearing and what else happens

I noticed something weird while playing the testing branch. The process bar of a job randomly disappear. It first happened while playing survival and a dupe started building a thermo regulator without a bar below the building appearing.

Then it seems it's not only building errands and it seems kind of random. In this case dupe couldn't follow the "move to" command while the process bar disappeared as the fabrication errand was in process (the blueprint of the building is irrelevant. It happens on the default building too)