Do you get the same result from a landline to landline ? or is this simply network to network conversion.
One thing you could try is:
On the PBX >> Trunks >> FXO gateway settings >>PSTN Gateway Options.
Try changing (and re-provisioning the gateway) with "Dial Delay" from "Wait for Dialtone" to "Dial after 1 second".
Failing that as always get me some logging, I highly doubt this is a Patton issue but if it is they will tell us what is going on.
enable
show running‐config
debug call‐router
debug call‐control
debug ccisdn signaling
debug context sip‐gateway signaling detail 5
debug context sip‐gateway transport detail 5
debug context sip‐gateway error