Can no longer query MongoDB Atlas documents in a cluster using an old .NET Driver 1.11

I am using a rather old C# driver1.11.0 , but until 3 days ago hadn’t any issues with basic query operations, i.e. retrieval of all documents in a collection. Now collection.FindAll() returns a cursor with 0 documents all the time, although I can see there are documents.

The current version of the free cluster is 5.0.9 and I’ve tried locally to setup a 5.0.9 instance in a Docker container (single server) and the same old driver works fine with it.

I don’t have a clue what might be the problem and how to detect what has changed or what’s special about MongoDB Atlas deployment. Could it be something cluster-specific?

The connection string in the .NET code looks like this:


The only thing that I found in the compatibility notes that sounds relevant was:

Starting in MongoDB 5.0, certain database commands raise an error if passed a parameter not explicitly accepted by the command. In MongoDB 4.4 and earlier, unrecognized parameters are silently ignored.

But this doesn’t explain why I don’t have such an issue with 5.0.9 outside MongoDB Atlas context.

Any ideas what might be wrong or how to narrow down the problem further?

Just for the record, newer versions of the driver successfully retrieve the documents, but the 1.11 doesn’t. It correctly returns the number of documents in a collection, but the documents are not returned in the cursor. This happens silently - no indication of an error.