I have an issue where when a call is made from an external caller to a phone with call forward all on to another external number it doesnt work. Where if a call is made from an internal phone it works fine.
Debugs and Config attached.
I found the solution but I don't have a Pri, I have an Isdn, even If the problem was the same.
Try to put this command under your interface Pri:
isdn map address .* plan isdn type unknown
Let me know If this help you.