That’s been discussed a couple of times in the last few months and has to do with the changes that smartthings is making to the way it handles Zwave security as it gets ready for the rollout of S2 support.
It still doesn’t have anything to do with SUC and SIS, it has to do with secure messaging.
I’m not feeling very well today and this is a pretty complex area, and besides I honestly know very little about how the SmartThings zwave platform has implemented the manufacturer controlled aspects, So hopefully other people will be able to assist you further.
See the following thread for discussion of when people first started seeing this message: