I did try the shift legacy / modern flight model, but no luck 
Helicopter are not easy, but seeing this level of uncontrollability is really unexpected (watch the video above until the end, i have the exact same thing happening to me, and that feels crazy if this behaviour is realisticā¦)
Anyway as @Olle2011T suggested Iāll keep the cyclic assistance on to remove that frustration, hoping for the bug to be reproducedā¦