I'd like to make sure that you'll be able to view all your vendors' names on the Online Bill Pay page.
Being unable to see all your vendors' names on the Online Bill Pay page can be caused by the stored data on your browser. Your browser stores cache for increased loading performance, but too much may lead to usual behavior like what you've experienced.
To fix this, let's access your account from a private window. It allows you to open QuickBooks with a fresh slate.
If can now see all your vendors on the Online Bill Pay section, I suggest going back to your regular browser and delete its cache. Doing this will helps you prevent this issue from occurring again.
However, if the problem continues after performing the steps above, I suggest contacting our Customer Care Team. They have necessary tools like the screen-sharing session, that can help determine the root cause of this matter.
Lastly, you can refer to these links I've attached to learn more about paying bills and on how Online Bill Pay works in QBO: