I've got similar issue with a new firmware. I went through all the latest 9-x-x ones (hoping to resolve DND button doesn't send SIP Response 486: Busy here) but config file from working 8-5-2S does't register with PBX. The last working one for me is SIP41.8-5-4S but still DND problem is not solved.
So, I'm not sure if config file's semantics changed again or the new firmware is just not compatibile with my Asterisk anymore. Debugging phone's logs there is one error: "ccsip_register_send_msg: Error: cc_cfg_table is null."
Googling this, points only to one blog with the same issue indicating a firmware bug. Hopeless situation.
I noticed, by changing this true
in SEPxxx.cnf.xml to "false" allows me to make calls but phone is obviously unregistered. Once I changed it to "true", phone status stays: Registering...
for a couple of minutes and then fails.