Hey @wiliam_buzatto,
Thank you for reaching out to MongoDB Community forums.
I suspect it might be related to the upgrade process, as there is a brief downtime when upgrading from M2 to M5. Please refer to the Modify a Cluster - documentation for more details.
Alternatively, this issue might also be related to one of the bugs we recently addressed, CSHARP-4001. A solution for CSHARP-4001 has been included in .NET/C# Driver 2.15.0. Please consider upgrading and let us if this resolves the problem.
If the issue persists, please share the MongoDB version, the driver version, and the code snippet you are executing, it will help the community to assist you better.
Best regards,
Kushagra