every time i press F3+F the game improve chunks number but when it arrives at 16 it stops. if i try to put 16+ chunks in the menù everything it's ok, but when i press F3+F the number goes back to 16. any fixes?

what version? and what mods are you using?

I had the same issue while using multimc. My RD would cap at like 19 and wouldn't let me go higher. I allocated more storage to the instances and that fixed it.