In my computer management console I can see two users P_FSSUserffffffff and S_FSSUserffffffff and they are in group FSSGroupffffffff.
There are also some more groups starting with WF-App following some random numbers. For example WF-App-4294967295-c983f0a0ccb3235a199072e7538a3bb4.
Seriously. Any documentation on that? Does Service Fabric rely on these users?
Those two accounts (S_FSSUserffffffff and P_FSSUserffffffff) are used to ACL shares used by ImageStore to copy files securely between nodes.
https://github.com/Azure/service-fabric-issues/issues/153