Just curiousity really, but I noticed in the recent days that one of my posts How to influence the position of float environments like figure and table in LaTeX? get plus/minus 10 point votes recently (which I find a bit surprising) - could it be that I have hit an absolute limit with 420 plus votes?
No, the ceiling is far higher... if there exists one.
What's happening is that some users have un-upvoted your answer and then re-upvoted it. Looking at your reputation for today, you'll see the following:
The -10 reputation stems from an un-upvote (actually upvoted on a different day) while it seems the un-upvote was immediately rectified (seconds apart) with a re-upvote. The re-upvote, of course, cancels the unnecessary un-upvote.