I noticed that my donator wings were not showing up so I looked into it and they're not being added until you enter single player - it is possibly fixed in later versions but I'm running 1.10.2-2.0.6.157.

Have you checked if your wings are just disable when you join a server? The state is now saved server side and its possible its set to disabled by default.
Edit: Ok never mind...

This should be fixed in the next release.