When executing an Insert with a Guid as a key, a select statement is appended to the query:
sb.Append(";select '" + idProps.First().GetValue(entityToInsert, null) + "' as id"); (https://github.com/ericdc1/Dapper.SimpleCRUD/blob/master/Dapper.SimpleCRUD/SimpleCRUD.cs#L403). The corresponding line is missing in the async code (https://github.com/ericdc1/Dapper.SimpleCRUD/blob/master/Dapper.SimpleCRUD/SimpleCRUDAsync.cs#L282).

I guess the select statement is (or was) used to get the return value, but it's not needed (as we can see with the async version). This can lead to problems because the query stops being completely parametrized:
insert into [FooTable] ([Id], [BarValue]) values (@Id, @BarValue);select 'some-explicit-guid' as id

I suggest to completely remove the select statement. Should I create a PR?