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A few days back, my reputation was 931. However, each day I found it going down by 2, and now it stands at 919.
Can anyone account for this loss? It seems no one has downvoted my answer or question as it doesn't cross up in the achievements.
You have previously edited 6 questions and got $2 \times6=12$ reputation points. Later these questions were deleted, thereby canceling the previous gained $12$ reputation points. See e.g. this & this mother meta posts.