Sorry for the very late reply, I haven't been able to play the game in a while. What I mean is that while my sim is at work, or sometimes between shifts, their coworkers/boss will be randomly removed from the relationship panel as coworkers and I can't use the tones to interact with them. They will be randomly re-added as coworkers later only to randomly be removed again. Like, for example, my sim has 3 coworkers and a boss; the boss and 2 coworkers will randomly disappear from the panel then several hours later 1 coworker will be re-added, then they'll all disappear, then maybe just the boss will come back. It repeats this every couple of hours with a random result on who'll be re-added or disappeared. There's no rhyme or reason to it.
Hmm, looking over the thing, I see that one of the criteria for interactivity is that the coworkers have to actually be at the office for you to interact with them there. Is the trigger of them leaving perhaps them leaving the office?