Created a simple “State Tree Property Reference” variable in a task, set it to bool, and am trying to bind it.
The second I click it before even trying to set a variable (or before any interface displays) it crashes due to the type not matching.
StateTreePropertyReferenceHelpers.cpp line 200
check(SourceAddress)
It’s null…of course because it has not been set.
Blueprint
Click here to crash:
I’m getting this same crash. I don’t think its the bool value causing the problem. I believe this happens when you try to assign a StateTreePropertyRef and there is a uObject reference somewhere in the stack of variables. In my case, I had a previous task in the same state that had a uObject output ref, once I removed that task it worked. I’ve seen the same crash if you have a uObject as a parameter of the stateTree.
Also, I searched for info on this crash while writing my own, nearly identical, set of “Set Param Ref” tasks 
it seems like updating stateTree params is a common pain point.
I had this same problem. Updating from 5.5.0 to 5.5.4 seems to have fixed it. Though clicking “promote to parameter” still caused a crash (albeit a different one: Assertion failed: Count>=0 [File:D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Public\UObject\UnrealType.h] [Line: 3984]), but creating a parameter manually worked and I was finally able to bind it without the engine crashing.
