Most of the solutions you will find on this subject is that there is a missing footer code but if you are also unable to load the theme customizer, let do it the other way around.
1. Check your Website URLS
Go to your WordPress Settings > General and make sure that your WordPress Address (URL) and your Site URL are a exact match.

2. User setting
Go to Dashboard > Users > Choose your user and make sure that the Toolbar option “Show toolbar when viewing site” is checked.

3. Missing Footer code?
Got to your theme’s footer.php file using a FTP client or in the WordPress Dashboard, go to Appearance > Theme Editor > find your footer file to check.
Look if you see the <?php wp_footer(); ?> code. It should be in the line just above the </body> tag. If it’s not there, past it, save and check if you can see your admin bar.
For a more detailed description this method, check out this tutorial on WP Beginner.
Searches for this problem can also be phrased as: