There was such a problem. I made an animation in Blender with two objects and one bone (platform and spikes). Combined it all into one object and animated it. When I exported to UE4, I was faced with the fact that the spikes move with the platform. The platform has received animation like spikes. How can this be fixed?
One thing that sticks out as odd to me is that you are using one bone. I don’t know if this is required, but I go by a 2 bone minimum - the root and the one that animates. You can weight the platform to the root and the spikes to the animating bone and the problem should be cleared.