Project played fine in 4.16 including packaged build. After updating to 4.16.1 today Standalone crashes every time. PIE etc. still work fine, successfully cooks & a packaged build does not crash.
and I get: Undo Spawn Play From Here Start
Issue reproducing when returning to old save file. Seem to be able to modify blueprint, character or UI. Will consistently start crashing standalone again however I cannot pin point particular actions I can take to reproduce. Leads me to think possibly game instance/modes or states communication with either playerBP or UI as the problem?
I have the same problem.
Works with different default pawn class. So it is something to do with my character class however I cannot figure out what. Any Idea be great!!
Check if changing default pawn class solves it if you are using a custom character BP. Can see if we are dealing with the same problem. 
Components within Character BP where colliding with each other. In this case multiple static meshes that where for some reason set to Block all Dynamic, GenerateOverlapEvents True.