I am a pretty new contributor so forgive me if this is some common phenomenon. I was writing an answer a few minutes ago on MathSE, but when I opened my profile to check on my reputation, there was a weird increase in my reputation (from 481 to 531) with no indication in my reputation summary (no new upvotes or downvotes). Also, when I checked on my account section from other sites, I found that my reputation was still 481. Is this a bug or something else?
Reputation scores are currently in flux because reputation gains for past question upvotes have been increased from +5 to +10. See this blog post and this question which explains a little about how it's being rolled out.
It's being calculated site-by-site and so rep will be in flux for a day or so while the servers work out - a little more on that here.