QueryMultiple with Multimap callback Func not called

I have followed #452
My callback Func never gets fired and the async Task I am running this inside gets returned early.

The only partial solution I could seem to find was: #727
But that doesn't seem to line up with #452

After this I am running into what I gather is a false error:
ArgumentException: When using the multi-mapping APIs ensure you set the splitOn param if you have keys other than Id Parameter name: splitOn

using (SqlMapper.GridReader reader = await connection.QueryMultipleAsync(query, new {id = id}, commandType: CommandType.Text))
{
    while(!reader.IsConsumed){
        var stuff = reader.Read(exerciseFunc, splitOn: "id").AsList();
    }
}

Edit:
I should note that the queries in my querystring operate fine if they are executed separately using connection.QueryAsync with the same callback Func

Start with the QueryMultipleAsync and GridReader.Read multi-mapping APIs shown in the report, then compare their behavior with QueryAsync using the same callback Func. Reproduce the reported early task completion and splitOn ArgumentException with the missing query and callback details; done means the callback behavior and splitOn handling are explained or corrected.