"Function ____ called from ____ should not be called from a Blueprint"

I don’t think that Parent::DampenInertia is callable. In my opinion the C++ implementation is only in case the blueprint doesn’t implement it (as replacement). So as soon as you implement it, your C++ implementation is gone.
Try to use an overridable kind of exposure if you want to get your C++ code executed, like BlueprintImplementableEvent.

That is only my thought maybe it works.

I’m getting the above error despite having the following in my C++ code, not in any protected or private areas:

/* Dampen the inertia of the ship to 0. Returns a dummy value. */
UFUNCTION(BlueprintNativeEvent, Category = Flight)
UINT8 DampenInertia();

I also have the function with DampenInertia_Implementation in the .cpp file, but I get the error in the title whenever I try to extend the function in a blueprint and then call that extended function.

Any help would be appreciated!