Getting 404 is a very common issue for custom post types regarding their single post. But this can be easily solved by a simple technique. Please check the following steps-
Step 01: Go to the WordPress admin panel Settings >>Permalinks.
Step 02: Go to the bottom of the page and click the Save button.
Step 03: Go to any single knowledge base post. You’ll see the 404 issue has been fixed, and now everything is working fine.
Note: From version 1.1.7, the plugin can automatically handle a single post 404 issue.
You can check the following video tutorial for more details-