Great job in performing some steps to fix the user issue, @tzykid.

Data damage on the company file can be the reason why the user access was changed to switch to single-user mode.

To fix this, we can run a file doctor to the affected company through the host company file. This resolves unusual behavior while working on the company file.

Here's how:

1. Download the QuickBooks Tool Hub file. .
2. Open the file you downloaded (QuickBooksToolHub.exe).
3. Follow the on-screen steps to install and agree to the terms and conditions.
4. When the install finishes, double-click the icon on your Windows desktop to open the tool hub.
5. From the tool hub, select the Company File Issues tab.
6. Select Run QuickBooks File Doctor. 
7. In QuickBooks File Doctor, choose your company file from the drop-down menu. If you don’t see your file, hit Browse and search to find your file.
8. Press Check your file and then Continue.
9. Enter your QuickBooks admin password and click Next.

I'm including here a link that provide a video tutorial of this process: Utilize the QuickBooks File Doctor

If you encounter any errors while working on a multi-user mode, I have here some resources that you can check out for troubleshooting steps:

• Resolve network issues with QuickBooks File Doctor test results
• Fix company file and network issues 

You've got me here to provide further assistance if there's anything else you need. Just let me know by dropping a reply below. Happy Holidays!