Ok ty. I will try to confirm it myself today by using your method.
But still I fell like there used to be mobs around every corner before, but now rates are very low (1h mineing session = 5 monsters)
Ok I managed to fix it. Created new world with same seed. Copied everything from old world except for level.dat, changed few parameters with nbt so that it maches my old world and it works great n
[media]ow.
Mobs spawn normally in new world. With local difficulty of around 2.
Can confirm sounds work. But standing in the dark for so long to play cave sounds explains why I never hear them. There is always some light around, especially in new caves. Mybe this needs to be adjusted.