What that likely means is that just over 30 days ago you got two upvotes. That no longer goes into the 30 day but still counts towards your total. I would however recommend strongly on focusing more on the message that your karma sends overall in terms of what comments have been received well and which have not rather than look at minor fluctuations.
Yeah, my 30 day karma went down, got −2 but my total karma was unchanged. Weird. Had −42 now it’s −44 and my total didn’t change at all.
What that likely means is that just over 30 days ago you got two upvotes. That no longer goes into the 30 day but still counts towards your total. I would however recommend strongly on focusing more on the message that your karma sends overall in terms of what comments have been received well and which have not rather than look at minor fluctuations.
Maybe the values are cached, and recalculated at different moments.