Hello @Andrzej Wysocki ,
Thank you for posting here.
To better understand the question, please confirm the following information at your convenience.
1.Based on "What could cause dsa.msc, the Active Directory Users and Computers snap-in, to start after 5-10 minutes?", did you mean you can open ADUC, but every 5-10 minutes, ADUC will be automatically start again?
2.Based on "It cannot be opened.", what error message did you receive when you open ADUC?
3.Does this issue appear as soon as the new domain control is promoted? Or is the domain controller able to work normally after being promoted, but this problem suddenly appeared one day?
4.Have you made any change before the issue occurs?
5.Can you open other AD tools(such as AD site and services or AD domains and trusts) on this DC?
Meanwhile, please check if any third-app/third-service caused the issue. You can perform a clean boot on this DC, then check if the issue persists.
How to perform a clean boot in Windows
https://support.microsoft.com/en-us/topic/how-to-perform-a-clean-boot-in-windows-da2f9573-6eec-00ad-2f8a-a97a1807f3dd
Hope the information above is also helpful.
Should you have any question or concern, please feel free to let us know.
Best Regards,
Daisy Zhou
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