The bug
The game freezes for 4 or 5 seconds or sometime crashes when going in the singleplayer menu in all the pre releases and in the release candidates. 

How to reproduce
Go to the Singleplayer menu in 1.18 release candidate 2 or any other 1.18 pre-release, or release candidate

The video end when the singleplayer menu loads.
There is 12 worlds in may save folder and my game is on a SSD

I now have only 4 world and i don't have any problems !