I Was Trying To Change Game Mode From Creative To Survival & When I Click Enter To Switch, The Game Will Crash. I've Attached A Video Of What Happens. I Use A Command Block So I Could See If It'd Work. (I Usually Get Over 100fps But It Was Low Because I Was Recording.)

UPDATE1
After Continuously Doing It, My World Now Loads Me Into Survival But Crashes Instantly.

UPDATE2
I've Just Loaded Another World & It Loaded Ok, With A Bit Of Lag.