Hi, @Proxi,
Welcome to the MongoDB Community Forums.
I understand that your .NET 6.0 applications running MongoDB .NET/C# Driver 2.15.0 are failing to maintain connectivity to your Atlas cluster while upgrading from M0 to M10. You also note that your services are running in Kubernetes.
This is unexpected. The 2.15.0 release included a fix for a DnsClient.NET issue that caused problems with DNS resolution in k8s environments. Subsequent releases have not included any additional DNS-related fixes. See CSHARP-4001 for more information on the DnsClient.NET issue fixed in 2.15.0.
I would recommend reaching out to MongoDB Atlas Support to assist in troubleshooting further.
Sincerely,
James