If bob is stumped there’s no hope for me!!
What server are you running (nginx, apache, lighttpd, etc.) and version?
What version of PHP are you running?
Server is Apache/2.4.34
Running php 7.0
Thanks
Andy
You don't have a CDN by something like Cloudflare on this site do you?
Check your vhosts to make sure you don't have contradicting rules. Make sure all your default .conf files are also redirecting to https. Let me know the results.