Stream CopyToAsync never returns

Trying to parse a csv file from a memory stream with csvhelper and since I'm using a stream I can't use a synchronous read. Originally I used the GetRecordsAsync method, but it would hang interminably. I figured it was an issue with the package and so decided to follow the advice of a similar post: Using CsvHelper with a Stream. However now it hangs on the stream.CopyToAsync(newstream) method. Furthermore signal R gives the following (unhelpful) error:

Microsoft.Azure.SignalR.ServiceConnection: Warning: The connection FDF6ub9XgExRg_etyA9NSgee127c661 has a long running application logic that prevents the connection from complete.

The csv file itself is 26 rows and 13kb, so it's not like it's doing some massive operation.

code is pretty much identical to that other post:

using (var newStream = new MemoryStream())
{
    await stream.CopyToAsync(newStream);   // hangs here and never returns. signalR disconnects, no Exceptions
    stream2.Seek(0, SeekOrigin.Begin);  
    ...
 }

So what's the deal is there some sort of configuration for SignalR I missed?