Job servers keep in "Update Running" state, and software version keep in "-1"

Hi experts,

I'm evaluating the approach of upgrading server from 7.1.6 to v8.

I deployed new servers with newer OS and SQL version, and restore the original DB to the new server, updated job server list and sync server reference in sync editor, reinstalled application server, checked data consistency, all seems fine.

However, in Job Queue, the jobs are not processing, and the job servers keep in "Update running" state with software version "-1". I browsed the job server in browsers, there is no error in the log, but just keep repeating info "Requesting process steps for queue \XXXX (job server name) / Last process step request succeeded."

Where can I know what was wrong, so that I may fix it? Please kindly advise.

Many thanks!