I noticed that my reputation jumped from 71 to 122. I didn't see any reputation changes in "reputation tab", until I unfolded reputation earned for 8 May.
There was something strange - "rep change":
What is it?
What can cause it?
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This happens when a post that gave you sufficient rep to give a bounty was subsequently removed.
After a rep-recalc, the system finds that you no longer had enough rep to "have given" the bounty. But of course it can't turn back time and change the past. Instead, it gives you that rep for free.
So a sequence of events such as this: (the exact numbers will be different for everyone)
Notice that you lost 100 rep twice (once from the bounty and once from the deletion). But you only had 101 rep prior to the bounty. That means that you'll have negative rep.
Since everyone has at least 1 rep, the system will "give" you enough rep to get back to 1. This would be recorded as a "+100 rep change".