I am using C# to develop a UWP app for Windows 10 running only on desktop computers, targeting platform version 10.0.14393.0. Due to business requirements, the app lifecycle
I remembered that previous SO post - His question was : When I use the App service to communicate with Win32 apps, it prevents the app entering suspend state. I've succeeded to recreate the issue with the sample app that referred at the post.
I don't now that is an intended behavior or not, but it may help to resolve your situation.
UWP application not going to suspend state