It was a couple of years ago, but the Go gRPC library had pretty broken flow control. gRPC depends upon both ends having an accurate picture of in-flight data volumes, both per-stream and per-transport (muxed connection). It's a rather complex protocol, and isn't rigorously specified for error cases. The main problem we encountered was that errors, especially timed-out transactions, would cause the gRPC library to lose track of buffer ownership (in the sense of host-to-host), and result in a permanent decrease of a transport's available in-flight capacity. Eventually it would hit zero and the two hosts would stop talking. Our solution was to patch-out the flow control (we already had app-level mechanisms).

[edit: The flow control is actually done at the HTTP/2 level. However, the Go gRPC library has its own implementation of HTTP/2.]