Explain Code Execution and Bottlenecks

Motorola's device management backend has this service, which pushes a firmware update to every radio in a fleet that is currently reporting outdated firmware. A candidate is shown the code below on a shared screen.

public class FirmwareUpdateService
{
    private static List<Device> updatedCache = new List<Device>();

    public void UpdateOutdatedDevices(List<Device> fleet)
    {
        foreach (var device in fleet)
        {
            SqlConnection conn = new SqlConnection(connectionString);
            conn.Open();

            var details = GetDeviceDetails(conn, device.Id);

            if (details.FirmwareVersion < latestVersion)
            {
                try
                {
                    PushFirmware(device.Id, latestVersion);
                    updatedCache.Add(device);
                }
                catch (Exception)
                {
                }
            }
        }
    }

    private DeviceDetails GetDeviceDetails(SqlConnection conn, int deviceId)
    {
        var cmd = new SqlCommand("SELECT * FROM DeviceDetails WHERE DeviceId = " + deviceId, conn);
        return MapToDeviceDetails(cmd.ExecuteReader());
    }
}

Based on this code sample, explain the execution flow in detail and identify every possible bottleneck or defect you can find, for a fleet that can have upwards of 50,000 devices.