Coming from 8.10.2 our upgrade process got stuck for unknown reasons so we engaged support and they helped us upgrade it starting from the web ui and upgrading the primary went fine but it did not progress through the second and third node. From here we uploaded the PAK file to both nodes into /tmp/ and connected with PUTTY to start the upgrade locally and push it through with this command :
after starting it you can see it rebooting and coming back with the new version. then you can start it from the last node and wait for the web ui to report it complete, it might take a bit to realize that everything has upgraded so give it some time and it might also reboot or restart some services on the nodes. for me it took like 15 minutes to fully become stable and done!