In order to narrow down the issue, would you please help collect the information below?
1.Did the current user exceed the maximum number of SSTP connection?
Based on the number of your VPN clients' connection, you can change the port number to 250 and then see if the issue is gone.
2.Did all the user disconnect VPN connections after 60 minutes? Or just some users?
3.Did you configure NPS to perform authentication?
4.Have you installed any third-party software in your environment?
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