digit falling off the TN user part in the request URI on egress

 

I have a simple setup for completing SIP calls. The ITSP routes calls to the waiting SBC/4500, all incoming traffic is forwarded to the Asterisk PBX, and the calls are terminated to the phones. Though things stopped working and while I can decipher the symptoms, I need help with identifying the cause.

 

In the log capture in sipmsg.log, when I compare the SIP INVITE message that was received in to the SBC with the one that was then passed on to the next hop (Asterisk), the single digit in the middle is missing.

 

Here is the starting couple of lines from message received into the SBC: