Started a new world and at the first night my fps was dropping a bit again but not as terrible as the last 2 worlds. But I did notice I had F7 enabled somehow during the night by accident which caused some fps loss yet not as severe as before. It wasn't enabled since the start though but fps lost due to this is totally my own fault for enabling this on accident. But beside that I also started getting some block lag. Blocks I mined were returning back. It felt like the local single player server was losing performance and getting behind. Even after disabling F7 thing again the block lag was still present for quite a while. Now daytime passed a little everything became stable again. Will edit shortly what happens in night 2 if I can spot anything.
/edit
Didn't make it to night 2 yet and block lag is still present, can barely mine anything even when I don't have fps issues.
Also before night 2 happens my client seems to freeze for some seconds when:
- opening a crafting table and
- eating food.
NEI searches become quite slow too.