Tess Ferrandez, a Microsoft software engineer, presented on diagnosing and troubleshooting issues with .NET Core such as high memory usage, crashes, exceptions, and poor performance on Linux, macOS, and Azure. The presentation covered tools for debugging memory issues, including dotnet counters, dotnet gcdump, and dotnet dump. It also provided demonstrations of memory issues, high CPU usage, hangs, and crashes along with the recommended tools to diagnose each type of issue.