So I followed directions in "Adding theme settings (advanced)" but for the life of me I can't find any page with theme settings. Is theme-settings.php still a thing?
If you are creating a custom theme then yes I think that file can still be created the same way as in D7. You could take a look at the Bartik theme in core.
PHP Openssl is missing perhaps?
I know you've stated that it's there, but if it's having issues loading for any reason, it will fail with updates.
Try doing a phpinfo(); call to check...
It seems that the redirect behavior either was or can be overridden with Rules.
We were able to keep people on the same page by creating a rule that sends them back to the original page...
Comments
If you are creating a custom theme then yes I think that file can still be created the same way as in D7. You could take a look at the Bartik theme in core.