I am not sure that this is a Kickstart/restore issue, but I'm asking in the hope you've seen this issue before and know what it is.
I'm moving sites from one VPS to a new VPS. This particular site is a sub domain (no issue restoring another site to the VPS). All appeared to be working, but if I try to access the admin area using https the admin template doesn't load. I can access admin using http, with no problem.
VPS has cPanel and CloudLinux
Backup was downloaded and uploaded via FTP
Hosting account was on PHP 8.1 but changed to 8.0 so as to be sure that DNS had propagated and I'm looking at the correct site. NS were only updated for the VPS 8 hours ago, so could this be the issue? (VPS using same domain, NS and hostname as previous VPS)
I've replaced the site htaccess file with the default Joomla 4 htaccess
I have switched off the http headers plugin
I have tried disabling gzip and reneabled. gzip is enabled in cpanel.
Error reporting is set to maximum and I'm not getting any errors
Cleared browser caches, tried with multiple devices etc.
BUT, if I enable Debug System, then the admin area DOES load the admin template in https. Switch Debug off and it doesn't load.