TLS handshake only 2RTT on Private Instance


I’m using WPT Private instance with agent (Win7) running in VirtualBox in Ubuntu 16.04. WPT is 2.19 and agents are up-to-date.

The problem is that I constantly see at least 2RTT TLS handshakes in results, while testing from Public (NL, IISpeed) shows me 1RTT TLS (using TLS false start).
Tried Chrome and Firefox - the same.

In attachments waterfalls from public and private instances.

Is it possible to fix somehow?