@Yuri_Rage said it BEST in a different thread…
"Please seek professional, possibly paid help to tune this Copter. Issues this severe + stabbing in the dark to solve them could kill someone.
@amilcarlucas provides services like this and/or can point you in the right direction.’
Even though it looked like it flew well for a few flights there is a lot in the background that you aren’t seeing.
At a min tune your copter with Methodic Config before flying again.