In 14.2 there is a new command: xcommand forcesystemkeyupdate  from CLI that clears this warning without rebuild.See: https://www.ciscolive.com/c/dam/r/ciscolive/global-event/docs/2022/pdf/BRKCOL-2060b.pdI just did it and it worked. 

Looking at logs. Found the same lines.Answer: CSCuo42486  Workaround:- None- The error is cosmetic and can be ignored   

 For CUCM and Unity Connection bug description has been updated, COP file fixes listed releases. So you can upgrade to any of these releases and then apply COP file.https://tools.cisco.com/bugsearch/bug/CSCur00930Downloads HomeProductsUnified Communi...

Leo, Do you have reference for this. Still murky waters:In 9.1 release Stratum 5 no longer enforced. http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/rel_notes/9_1_1/CUCM_BK_RD7D4696_00_cucm-release-notes-911a/CUCM_BK_RD7D4696_00_release-notes...