Thanks !
problem appears to involve not having a PrimitiveComponent as root when you brought project over from 4.5.1, in which this was not an issue. Unfortunately, adding a PrimitiveComponent and making it root does not solve issue, and only replacing ProjectileMovement component will fix things.
I have entered a bug report for this issue (UE-5548) and I will let you know when I see an update on it. Thanks for report!