gRPC client receives Http2StreamException from gRPC running on Kestrel server

I have gRPC server on Kestrel and test client on WinForms. Both netcore 3.1. On separate request all Ok. When I start multiple parallel requests I see error below:

Status(StatusCode="Unavailable", Detail="Error reading next message. IOException: The request was aborted. Http2StreamException: The HTTP/2 server reset the stream. HTTP/2 error code 'INTERNAL_ERROR' (0x2).", DebugException="System.IO.IOException: The request was aborted.
 ---> System.Net.Http.Http2StreamException: The HTTP/2 server reset the stream. HTTP/2 error code 'INTERNAL_ERROR' (0x2).
   --- End of inner exception stack trace ---
   at System.Net.Http.Http2Connection.Http2Stream.CheckResponseBodyState()
   at System.Net.Http.Http2Connection.Http2Stream.TryReadFromBuffer(Span`1 buffer)
   at System.Net.Http.Http2Connection.Http2Stream.ReadDataAsync(Memory`1 buffer, HttpResponseMessage responseMessage, CancellationToken cancellationToken)
   at Grpc.Net.Client.StreamExtensions.ReadMessageAsync[TResponse](Stream responseStream, GrpcCall call, Func`2 deserializer, String grpcEncoding, Boolean singleMessage, CancellationToken cancellationToken)
   at Grpc.Net.Client.Internal.HttpContentClientStreamReader`2.MoveNextCore(CancellationToken cancellationToken)")

I need suggestions.