It just happened to me as well with FSLogix. I'm trying to stay away from Writables but we do use appstacks. I updated my image and Sticky Notes, Snip & Sketch and Calculator disappeared. I was the only one that logged in after publishing to the pool so I reverted back to previous snapshot and published that to the pool but my UWP apps are gone now. Other users don't have that issue but again they didn't sign in to the pool after update. Logging in to another pool with different image didn't seem to help. I believe in my case I need to delete my FSLogix profile and then I wil lhave them back. In your case deleting writable is probably gonna fix it.