I appreciate you taking the time to complete the steps to remove user access, @jmcampoverde. I am here to provide you with the solution to the issue you're encountering.

Have you tried it in a different window to see if you get the same results? The high amount of data in the cache is most likely the cause of QBO's sudden failure. These will continue to acquire data and will not clean its history automatically. Follow the procedures below to correct it: 

1. Restart your browser.

2. Log in to your account and delete the user in an incognito or private browser. You can use these keyboard shortcuts to launch a new private window:

· Google Chrome: press Ctrl + Shift + N  
· Mozilla Firefox: press Ctrl + Shift + P
· Safari: press Command + Shift + N

3. If it works on the private browser, you can go back to the regular browser and clear your browser's cache.

4. Then, delete the user again using your regular browser.

Moreover, I'll leave here an article for additional guide on how add and manage users in QuickBooks Online.

Please don't hesitate to post in the Community if you require support. It gives me great joy to support you. May you have a fantastic day