There's the occasional bug in my game where a Sim's career and career history are deleted and the Sim is reassigned a job in the Law Enforcement career as a Snitch. I'm not sure what causes this. But the last time it happened was when I had to reset one of my Sims with NRaas' Master Controller. Because I'd accidentally told her to age up when I had the wrong Sim selected.

My main concern with this is that when I restore the Sim's correct career track and career level, they have to wait at least a day before they can go to work, even if they otherwise would have been able to go to work that day.

Does it always happen after a sim is reset through Master Controller? I've never experienced this, but I also don't use MC's sim reset functionality much.

If it's just after reset, I'd say it sounds like a side effects of the reset... I've recently had some weirdness when using Reset Everything through which I've learned that losing data after "Reset Sim" (and "Reset Everything") is sort of expected. See a somewhat related thread at NRaas forums.

I'm not entirely sure. I just wish there was some way to prevent it from happening. Since it means that when a Sim's correct career data is restored, they generally have to skip a day of work. As Sims can't go to work on the same day they got the job. The same thing happens when a toddler becomes a child or a child becomes a teenager. They can't go to school on the day they aged up.

Do you have Overwatch installed? In it's setting there must be something about resseting careers progress, but I'm not sure if is there is such an option.
Do you have mods that alters careers like Story Progression (I'm not familiar with SP) or perhaps a mod conflict?

I have Overwatch installed, indeed.

The only mods I use extensively are a bunch of NRaas mods and Pescado's AwesomeMod.

It also happened again today which really ticked me off. I ended up having to give the affected Sim a promotion since she definitely would have gotten a promotion later that day, had she not suffered from this glitch.

I've just noticed how the glitch only seems to be targeting Sims in a specific household.