Connection strings using an authentication type that System.Data.SqlClient doesn't recognize will break in SqlErrorLog.cs. For example trying to connect via Service Principal to an azure db;
"connectionString="Server=tcp:ServerNameHere.database.windows.net,1234;Authentication=Active Directory Service Principal;..."
Not sure how this gets resolved but by replaceing System.Data.SqlClient with Microsoft.Data.SqlClient in the usings of SqlErrorLog.cs. Apologies if this isn't the right place to bring this up.