Sure, if the tuning peg is slipping. I have an old harp that every once in a while one of the bass tuning pins just lets go and the string goes completely slack. But it is easy to figure that out because the pin itself turns very easily. I really should fix it, but I rarely use that harp so I just haven’t been bothered to.
If the tuning peg is still tight in the hole then you might have someone messing with you. That or you aren’t securing the string on the tuning peg. When you wind the string do you tie it, or wind the string over the loose end a bit? If not then the string could simply be slipping through the hole in the tuning peg and loosening up.
Could it be possible that there was a lot of winding to the string on the tuning pin? I’ve seen that happen before. Too many turns can cause the string to get too close to the edge of the pin, and then just a small jarring can cause it to slip off. You might want to check your other tuning pins for this.