This is madness!
I just added UPROPERTY line, recompiled it. And blueprints do not set that to nullptr
UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "_K2G|CelestialBody")
UStaticMeshComponent* MyPlanetMesh = nullptr;
then i reverted it all to:
UStaticMeshComponent* MyPlanetMesh = nullptr;
Without UPROPERTY like it was before, now everything works again. Blueprints no longer wipe it.
So yes mesh component was there, blueprints just wiped this variable for some reason.