Here are a few steps you can try to fix QuickBooks running slow in multi-user mode:

1. Verify that all users are using the latest version of QuickBooks.
2. Make sure that the server computer meets the recommended system requirements for running QuickBooks in multi-user mode.
3. Check the network connection and network speed to ensure that it is fast and stable.
4. Verify that the company file is not damaged by running the Verify Data utility in QuickBooks.
5. Reduce the number of users accessing the company file at the same time.
6. If the company file is located on a network drive, move it to the server computer.
7. Make sure that the server computer has enough memory and disk space.
8. Check to see if there are any conflicting programs running on the server computer or client computers.
9. Run the Rebuild Data utility in QuickBooks to repair any data damage.
10. If the above steps do not resolve the issue, consider hiring a QuickBooks ProAdvisor to troubleshoot and fix the problem.

Please note that this is a general guide, you may need more specific troubleshoot based on the specific scenario.

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