In our company, we rely on CiscoISE for providing Wi-Fi BYOD service to company staff. We have more than 10 ISE nodes deployed in cluster Infra.
All ISE server nodes were on very old version 1.3. Each time we try to upgrade all ISE server node from version 1.3 to 2.4 by application upgrade bundle, at least on 2-3 ISE PSN nodes , application service will get stuck in "not running" while installing patch after upgrade and re-image was the only last option to recover from App data base lock error and it will next many more hours to troubleshoot and to get RCA.
As per my experience, It is best to re-image all ISE PSN server node to latest ISO version by CIMC and do patch install before registering ISE PSN node back to existing ISE Cluster Admin.
Please make sure to import/manual back-up of CLI Config and SSL cert from ISE-PSN nodes before re-image on ISO