Today after I updated to forge 12.18.1.2063 for MC 1.10.2.
If I tried to join my existing singleplayer world, the loading stops and I find the following entry in the log
This world was saved with mod Forge version 12.18.1.2060 and it is now at version 12.18.1.2063, things may not work well
So I go back to the 2060 version and the world is loading without problems
In my case the loading stops from the 2061 - 2063 version (I have checked that)
and I get a server crash rather than a client crash though it is a single player world
Edit: I forgot to mention that the client is freezing and the only way out is to kill the process
Latest log: http://paste.ee/p/GFLLH