I feel like I'm suddenly receiving noticeably less while mining the 31 algorithm. I tried to find a difficulty chart but I couldn't find anything, so I used calculators to see which algorithm is more profitable and it seems I was right, 31's profitability fell a lot.

Are ASICs introduced, at least officially? If not officially then I guess someone has started mining privately with them until they decide to sell them for "new" hardware.
Either that or suddenly everyone switched to 31 and Linux I guess... very unlikely!