The Certificate Expiry seems to be a bug and it was solved when I upgraded to CE9.2.4   https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvg46418/?rfs=iqvred  

Hi Russell,   Can you post a screenshot of the CUCM certificates in the security tab?   Thank you, Ton

Hi Russell,   Can you check if the device has a CUCM CAPF certificate?    I think the warning does not do a good job to tell what certificate you are missing. I have CAPF and I dont have that warning. Maybe just a shot in the dark, but hope you find ...