Did you configure permalinks yourself? I would recommend you to:
1. Make a backup of the htaccess file you have in your wordpress root
2. Navigate to the permalinks settings in the WordPress dashboard.
3. Navigate to the Permalinks settings in the WordPress dashboard and select “custom Structure” and enter the following: /%postname%/
I had already tried this resolution. But, the existing pages now give me a “This page cannot be found” error.
When initially setting up this WordPress site a couple days ago, I changed permalinks from the default to using the post name structure. Then, I notice it was adding index.php to the url and tried using the custom structure (same way you mentioned above). But, that broke the links to the pages.