This one has "Not Ready - Phone Working": https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/crs/express_11_6_2/maintain_and_operate/guide/uccx_b_ccx-admin-and-operations-guide/uccx_b_ccx-admin-and-operations-guide_chapte...

Did you by chance change from IPIVR to CVP?

Did you ever get a definitive answer to this?

Correct, here is the link: https://bst.cloudapps.cisco.com/bugsearch/bug/CSCuq45068/?rfs=iqvred   According to that bugnote it seems like it may be supported in 11.5, but I can't find a specific reference to that.

That's really all that would be expected to cause it. Your agents wouldn't necessarily notice if they aren't paying close attention or if it happens quickly. If they are on a call, a phone briefly deregistering won't even be noticeable as the voice c...