Theme Rendering Issues
If you are having issues with theme rendering particularly after restoring a site to a new server or using SSL then you might need to rebuild your theme CSS.
You will typical notice an issue on the homepage/login page where none of the images are rendered and the standard bootstrap CSS elements do not get applied and everything will be on the left hand side with no menus etc.
To rebuild your theme CSS use the following command from your moodle root directory:
Note this can take some time to run.