When disconnected from Ethernet, and connected to Internet, my RPi 2 is not recieving AirPlay content.
Is anybody else having this problem, or am I on my own?
Can you explain your problem a bit better please.
Are you saying that if you connect your Pi to Ethernet Airplay works, but if you connect to the same network using Wifi, Airplay does not work ?
If so you need to check your wireless router’s settings and make sure either multi-casting support is enabled or bonjour support is enabled - at the moment your router will be blocking the broadcast of bonjour messages.
Yes that is what i mean.
I have checked router settings, and both are enabled - Are any settings in OSMC/kodi blocking this?
No,
There is nothing in OSMC that will be blocking it. Just in case - have you tried rebooting OSMC after switching to wifi (make sure ethernet is unplugged) if it is still not appearing as an Airplay device it must be the configuration of your network - something will be blocking bonjour broadcasts.
This wording always makes me suspicious. Are you indicating that you are moving your OSMC from being connected to your LAN (Ethernet) to be directly connected to the Internet?
The first thing I did was reboot it 
Will recheck wifi settings tommorow. It actually 8:29 pm where I live!
Sorry, my wording was not clear enough. It is now connected to Internet whit a wifi dongle.
But, is this wifi network that it is connected to the same wifi network that your Airplay devices are connected to ?
Also check that you are not connecting to a guest network on your wifi router as this will block traffic between devices and only allow internet access. (Thus blocking airplay)
Bonjour only works across the same broadcast domain.
So you use Wifi Dongle instead of cable? But is the Wifi still your LAN (same as the one you connect to with cable/ethernet) or is a different network (e.g. direct public Internet)?
It is connected to the same network as all of my i devices are.
Unfortunately you are just going to need to do some troubleshooting on your network then to find out why bonjour announcements are not being forwarded.
A tool that can view bonjour announcements like “bonjour browser” in windows will help you to see what bonjour announcements are being sent on the network.
If you have access to a different model of access point to try as a test I would also try that. Check for firmware updates for your router as well.