Unity/WebGL Build Error for Gamelift Project – System.Configuration.ConfigurationManager::get_AppSettings

I’ve added aws gamelift plugin to our game (using this tutorial Integrating games with the Amazon GameLift Plug-in for Unity - Amazon GameLift).
While the game works fine in the editor, I am facing this error while running the game in the browser System.Configuration.ConfigurationManager::get_AppSettings.

Later I am getting an error

ArgumentNullException: Value cannot be null.
Parameter name: obj
  at System.Threading.Monitor.ReliableEnterTimeout (System.Object obj, System.Int32 timeout, System.Boolean& lockTaken)

right after calling new AmazonGameLiftClient(...)
But I am guessing fixing the first error might fix this too.

I’ve seen this post Unity/IOS Build Error for Gamelift Project -- System.Configuration.ConfigurationManager::get_AppSettings which talks about the same error but on iOS, but the suggested fix is downgrading the SDK to 2.0 which I think is really bad.

My link.xml:

<linker>
    <assembly fullname="AWSSDK.Core" preserve="all"/>
    <assembly fullname="AWSSDK.DynamoDBv2" preserve="all"/>
    <assembly fullname="AWSSDK.Lambda" preserve="all"/>
    <assembly fullname="AWSSDK.GameLift" preserve="all"/>
    <assembly fullname="AWSSDK.SimpleNotificationService" preserve="all"/>
    <assembly fullname="UnityEngine">
        <type fullname="UnityEngine.Networking.UnityWebRequest" preserve="all"/>
        <type fullname="UnityEngine.Networking.UploadHandlerRaw" preserve="all"/>
        <type fullname="UnityEngine.Networking.UploadHandler" preserve="all"/>
        <type fullname="UnityEngine.Networking.DownloadHandler" preserve="all"/>
        <type fullname="UnityEngine.Networking.DownloadHandlerBuffer" preserve="all"/>
    </assembly>
</linker>

Thanks for any help!

Eventually I switched to the JS sdk for the webGL build only, which works fine