Windows: WebEngine connections huge delays

Build simple program that used websockets to connect to my websocketserver. Server on address 127.0.0.1

I use WebEngine for viewing bug and WebView for control.
When network fully configured - setted real default gateway (and maybe something else) - all ok.
When network not properly configured - resetted default gateway - i see huge delays:

WebView: fast connection (fractions of seconds)

WebEngine: 5 second on every connect on test program. (up to 25 second on real application).

Chrome (load html-page with javascript directly) - fast connection (fractions of seconds).

Firewall are disabled.
Netcat fast connecting to server.

Changing server address from 127.0.1 for real network address not resolve problem.

When shutdown network interface - I see fast connect.

Its a really big problem because I don't see any doc for additional cooking
WebEngine for work instead official doc. where not described this situation.

Users cannot wait 5-25 seconds for establishing connection to localhost.