Sip over VPN no sound issue on Cisco 7940


We have a couple of remote phones connected in via VPN and I am having trouble getting them to register after rebooting them due to sounds issues. We are on FreePBX distro 10.2 and had some trouble connecting these phones up when we first moved over, after adding the remote network address to Asterisk SIP config they worked. Now, after a VPN reboot (this is the only change to the system) the sounds seems to have gone again.

The phones are accessible over the network and I can telnet to them and access their configuration settings and can confirm that they are pointing to the right server, have the correct DNS and TFTP settings. I changed the quality=yes to qualify=no and they appeared to be contactable but none answered so I don’t think they registered correctly and showed up as unmonitored in SIP SHOW PEERS. When they do register there is still only sound one way.

Under SIP channels I can see the Extension: 182 0120fd040e60095 0x0 (nothing) No Init: NOTIFY

Any ideas where to look next as I have run out?