I have tested quite a number of SIP devices against our UCx product line, but I had not heard of Revolabs before this post.
With that said, I may not be of very much help but let me try.
I am going to make a couple of assumptions -
first the phone does register correctly when you power cycle it
second when the device gets into this state the device can not see the UCx server - I make this assumption because if the SIP device could see the UCx it would still be able to make outbound calls without the device being registered with the UCx.
When you see the phone in this state, navigate to the PBX/Tools gui page and in the CLI field type the command 'sip show peers'
you will see the extension number and if it is registered you will see the ip address. if it is registered dial *65 on the device and see what extension is spoken to you. Does it match what you expect?
I suspect it won't show as registered. Now I would go to the Support/Packet Capture page, and start a packet capture, Cycle the Device and stop the capture when the device is online. Use wireshark to view the sip messages n the packet capture. Inspect the packets just to make sure there were no errors in the registration sequence.
My only other guess is that a timer is kicking in. and the only way yo figure out which timer is to monitor the device and see if it goes offline consistently at the same time after registration. Convert the minutes to seconds and look for a timer in the settings of the device that matches up to your calculations.
according to the manufacturer the default for the refresh timers is that the device send the options message to the server not the other way around.
let me think a bit more about this.
