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When I saw today it was 12xx something but now it has gone back to 914,2 days ago it was 989.
Is there is bug in the system? If so,how do I get my reputation back?
You can check https://askubuntu.com/reputation for a detailed report of changes to your reputation. (Source)
Probably those votes were invalidated by our daily vote anomaly detection script.
There are no known issues with the rep system, however, there are near-constant attempts to game the system.