UPDATE!
The 4.10.4 Hotfix is now live! This Hotfix corrects an issue that was unintentionally caused by the previous update. We apologize for any difficulties this may have caused.
Fixed in 4.10.4- CL#2872498
Fixed! UE-27124 Switching levels via blueprints crashes editor
REMEMBER: Please report any new bugs you find to the UE4 Answerhub “Bug Reports” section