How do I find PX4 firmware + Throttle problems

Hi Guys,
I have replaced the FC on my 680 Pro hex copter. I just bought a PX4 Kit from and also the telemetry radios. I am having trouble with the throttle setting, when I arm the drone and the motors start up I have to bring the throttle up to 50% or the motors shut off, if I go above 50% than the motors run up to full speed, if I then bring the throttle back below 50% the rpm slowly drops, but not in step with the throttle. All the way to down to zero the motors will finally slow and then stop.

I am using a PX4 FMU V5 with the matching GPS and radio link. The PX4 came loaded with ver 1.9 firmware and I messed up and loaded PX4Pro V1.10.1 firmware and I am wondering if that is the problem.
I am using Qgroundcontrol but have no idea about finding the newer firmware for the PX4.
I am using new FrskyTaranisQX7S with access protocol and a Frsky RX8 Pro with the access protocol as well. Any pointers would be great!