I have had a problem in version 5.15 with smart components disappearing from a smart component group.
I had 4 smart component groups each containing 10-20 smart components linked together and when i went to run the simulation I got no response back from the objects i expected to move, only to find that a number of smart components had completely disappeared. In one group the first 3 components had disappeared out of 10 and in a second component 8 components had disappeared out of around 20.
I am not sure if this is happening during testing or construction of other smart components or if this happened during saving then loading of the project as I only noticed this when starting the simulation after loading the project and then applying some changes