i have couple of snom D715 with firmware v220.127.116.11 and have been unable to upgrade them to the latest versions after several tries.
One other horrible experience i am having is that when two of these devices are set up on my home router, they seem to be very stable. but when two are set up on the LAN of my office, one of them keeps rebooting over and over again after displaying the message "new network policy".
this experience is actually the reason i have tried upgrading the firmware
Your advice will be deeply appreciated.
I have created a ticket for this issue. You should have received notification of it via email.