If it was a problem related to the key repeat rate, it would affect all of the keys. Tweaking the repeat rate might relieve the symptom, but will leave the problem to reappear later.
If it was a keyboard electronics problem, I would expect it to affect several keys on the same row or column in the keyboards matrix.
I would suspect the key itself, the physical button might well be returning to where it should be, but the thing that joins the two contacts together on the keyboard PCB might not be releasing quickly enough. If the dimpled rubber membrane for the full stop has gone a bit wonky, it is one of those "not consumer serviceable" parts, and can only be mended with a new keyboard. Fortunately, these are relatively cheap these days, and a USB one can work a laptop just as well as a "proper" PC.