This is happend to me twice now: I have a good working JSS where every client checks in, everything is good etc.
But some clients randomly stop checking in after I've upgraded our JSS to a new version. Happend to me at upgrading from 9.65 to 9.82 and now from 9.82 to 9.91. I'm managing 220 clients at the moment and 20 or so stopped communicating after those patches.
Since I'm unable to change the reported IP address so that can try to fix things using Casper Remote, I end up asking people to please swing by our IT Helpdesk so that my colleagues manually have to re install the client using a QuickAdd package.
Any ideas? I'm aware that the jamf binary upgrades itself after the first check in after a JSS patch and the only thing that I can think of is that this upgrades fails for some reason and breaks the whole binary.