6.0.1 fails to send MMS over PIA Always-On VPN when using 4G LTE Yesterday, I set up a PIA VPN. I've configured it to use IPv4 over T-Mobile 4G LTE. 

I'm unable to send or receive MMS while connected to the VPN -- they can be sent/received as normal when the VPN is disconnected. Any insight as to the origin or solution for this problem would be appreciated.

SMS works. Voice works. WiFi calling works. 


Using L2TP/IPSec PSK.
VPN server is configured on the Android device using IP, rather than domain name.
DNS server is also configured by IP
I have no L2TP secret.
No IPSec ID
Using IPSec pre-shared key
Not using any DNS search domains
No forwarding routes configured


I suspect there is some sort of configuration issue with my APN settings; the current configuration works when disconnected from the VPN.

** Update - I haven't yet found a resolution to this specific issue. After getting frustrated using the manual configuration in the settings menu I decided I would try their official Android app. It will set up the connection for you. Unfortunately, the currently version of the app doesn't expose what specific configuration it is using.
I've just found an issue in AOSP that tracks this and has a suggested fix for it:


  I tried Textra as a texting replacement app (for other reasons). In
  the settings it has an option to use either System or Legacy protocols
  for MMS. It even tells the user to try System if they have a VPN
  enabled. I switched to System from the default Legacy, and now my MMS
  works flawlessly with a VPN running.