Hello Gabriel Caicedo,
Welcome to the Microsoft Q&A and thank you for posting your questions here.
I understand that you are having an issue with three users where their Azure virtual desktop (AVDs) freeze or shut down unexpectedly, despite all your tries the problem persist.
One of the most common situations could be performance issues, follow a methodical approach to identify and resolve this common issues. This link: https://learn.microsoft.com/en-us/azure/virtual-desktop/troubleshoot-client-windows provides practical steps for AVD environments deployed in Azure.
Also, since only three out of many. Check for scheduled UI changes: https://techcommunity.microsoft.com/t5/azure-virtual-desktop/session-hosts-changed-from-unavailable-to-shutdown/td-p/3779776 and follow security best practices for AVD. Azure Virtual Desktop benefits from built-in advanced security features, such as Reverse Connect: https://learn.microsoft.com/en-us/azure/virtual-desktop/security-recommendations.
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I hope this is helpful! Do not hesitate to let me know if you have any other questions.
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Best Regards,
Sina Salam