Dave-XR500

If you are still having problems with your XR500 and iPhone RCS chats, you can always disable the QoS (and reboot router after making the change) inside the XR500 if that is something you are okay with (like I was mentioning in my previous post). Something tied to QoS is blocking the connection with iPhone RCS, which is rather suprising. I tried everything else (port forwarding to appropriate ports, etc.) and that was the only solution that worked for my home network.  I have everything else still enabled in the router, except for QoS being disabled, and my wife's iPhone has worked perfectly with RCS chats (since disabling QoS on the XR500). I had to reboot router after disabling QoS then it works great. 

I tried this, but there was no change. I double-checked my Geo-filter, but I do not have any devices there.
 
Then I saw this and tried it. This worked! However, a couple of my IoT devices could no longer see the network. I reverted the changes and rebooted my router. After that it was still working! Perhaps it was one of the previous attempts, and I just needed a reboot? I still have my ports and NAT open. 
 
Just want to say thanks now to all the suggestions. This has been plaguing me since September.

I just figured this out. Wife has a iPhone and I have Samsung. She has RCS but drops when connecting to just our router. Anyone's else's router is fine. We have a Netgear nighthawk and the solution is go to routerlogin.net when on the local WiFi and input your login info so you can change the router settings. Go to settings-vlan bridging- allow Port 1 and only the 2.4g (or you'll be factory resetting the router it has a bug) then apply and it'll reboot. RCS messaging is not longer an issue.