Extension InUse and DND issues


I have a weird issue happening with the latest build of AsteriskNOW and Polycom VVX400 phones. What is happening is this…at random, random phones stop accepting calls and sends the caller to voicemail automatically. The phone does not show that DND is enabled, but if I go into UCP, it shows that that extension has DND enabled.
I thought it might have been an asterisk issue, so I rebuilt the phone system and restored the extensions, time conditions, etc from the backup, to no avail. It is still happening.

Another thing that started occurring, is that one extension stops accepting calls and tells the caller that the extension is busy. When I checked the CLI and traced the call to that extension, I see the call going to is, but then I see the line that says that the extension is in use. However, if I reboot the phone, it starts working again just fine.

Any help would be greatly appreciated.

Thank you!