One of the projects I updated to 4.17, started getting the blueprints crashing on compilation issue as well.
For me the problem was with an inherited interface reference.
The class with the compilation issue, was referenced by an interface, which was in turn used by another class, which was inherited from by a child class. This child class had no reference to the class with the compilation issue, other than through inheritance.
The reference chain looks like this:
Here is another diagram, showing the same reference chain:
To fix the issue, I overrode the interface function in the child class to return the inherited variable,
essentially re-implementing the function from the parent class in the child class.
As @dzarafata said above, recompiling the parent class will allow the class with the compilation issue to compile, but only during that editor session.
It would appear then that the reference is either not being created, or being optimized away in 4.17.
So @dzarafata, if you try creating a reference to the “Pawn” in “Flashbang”, it might fix your issue.