[ikk157]

Well it depends, updating Debian to a next major release (version installed to version_installed+1) is not a critical process and you can improve your success rate by doing the update process on a fresh install of the OS.

I personally did it after the KVM refresh and it worked without any issue.

This tutorial is super detailed and if you follow it you will get a fully updated and working Debian

Well you just described one of the issues, you’ll need to request a fresh OS install to increase your success rate. Which brings it back to my point.

I personally believe that you shouldn’t upgrade unless you really have to. Will save the admins here a lot of work. 

It’s just not a risk worth taking if you’re just upgrading for the sake of upgrading.