Basically, this is all you need UFUNCTION(BlueprintCallable, BlueprintPure, Meta = (BlueprintThreadSafe), Category = “MyCategory”) and whatever else your function needs to be called with.
Unreal Docs Class Specifiers | Unreal Engine Documentation
"BlueprintThreadSafe
Only valid on Blueprint function libraries. This specifier marks the functions in this class as callable on non-game threads in animation Blueprints."
As everything that has a “Warning!” Label, Use with caution, Was having this issue in 4.2.6.2 following a tutorial on YT, Hope this helps another vigilant seeker, Happy Deving!