HTTP/2 client preface string missing or corrupt. Hex dump for received bytes: 00016501250000000180000000db02074f5054494f4e5341

Question

I'm trying to debug an HTTP2 connectivity issue. Strangely, the behavior that I observe on Google Chrome is that the Preflight (OPTIONS) fail intermittently. It fails for a while and then it starts succeeding.

Here is the net logs for the failing connection:

t=26715 [st=83]    HTTP2_SESSION_RECV_SETTINGS
t=26715 [st=83]    HTTP2_SESSION_SEND_SETTINGS_ACK
t=26715 [st=83]    HTTP2_SESSION_RECV_SETTING
                   --> id = "6 (SETTINGS_MAX_HEADER_LIST_SIZE)"
                   --> value = 8192
t=26720 [st=88]    HTTP2_SESSION_RECV_GOAWAY
                   --> active_streams = 6
                   --> debug_data = "HTTP/2 client preface string missing or corrupt. Hex dump for received bytes: 00016501250000000180000000db02074f5054494f4e5341"
                   --> error_code = "1 (PROTOCOL_ERROR)"
                   --> last_accepted_stream_id = 2147483647
t=26720 [st=88]    HTTP2_SESSION_CLOSE
                   --> description = "Connection closed"
                   --> net_error = -100 (ERR_CONNECTION_CLOSED)
t=26727 [st=95]    HTTP2_SESSION_POOL_REMOVE_SESSION
t=26728 [st=96] -HTTP2_SESSION

The code uses XMLHttpRequest to create this connection. The server I'm trying to connect is Alexa Voice Service (AVS). https://developer.amazon.com/en-US/docs/alexa/alexa-voice-service/manage-http2-connection.html

I tried setting up connection with Alexa through web browser, however connection PreFlight fails.