I flew my IRIS+ for the first time last week. I had a few successful flights including flying simple missions.
Upon a normal landing 2 of the motors stopped too early. Now if I try to start the IRIS+, the motors start one after the other as I increase the throttle. Obviously the copter is not flyable.
I tried reloading the parameters and calibration but this is not helping.
Something must have happened with your radio or ESCs.
I actually caused this issue by changing the trim on my radio. I wanted the radio calibration to be more close to center and my upper and lower numbers to be 1000 and 2000.
After doing a radio calibration the motors due just what you described.
To fix this you need to do an ESC calibration and maybe a radio calibration as well.