So try to figure out what’s happening.
If you force refresh the page is it the same?
If you view source in the browser do you see that your stylesheets are linked correctly?
If you view the Network tab of your browser’s developer console, do you see it requesting stylesheets? Do they succeed?
Is this failing page using the same template as ones that succeed?
What’s the difference in the html between the successful and failed pages?
etc