on my mobile I see I got a +1 yesterday. I looked at the question / answer and saw nothing different than the day before. ??? just curious.
For just one point, the most likely situation is: You spent 1 point on down-voting a question or answer. The user or a mod deleted the item. You were reimbursed the 1 point.
There could also be several changes rolled up into one: user "un-downvoted" one of your posts (+2), but you downvoted something (-1). Or other combinations.
As far as I can tell, there is no easy way to find out which question/answer was removed to cause this change. You might see +6 as the net change, +5 for question upvote, +1 for deleting an answer you downvoted; I don't know of a way to trace back where the extra +1 came from.