Swash locking up when flight modes are changed

I’ve have a 450 Heli with a pixhawk and Taranis Firmware updated to V3.4.4. I have setup the swash as per ROB’s Video

All has gone well, but if I change the flight mode from Stablize the swash moves down to the low position, and locks up.I have tried various flight modes.

Solved. You need GPS Lock