Piccolo hitting invisible wall in forward flight

When in forward flight, the piccolo seems to hit an invisible wall.

It will be flying forward in gym and nose will turn up and forward flight will halt, nose will drop and forward flight will resume. Does not matter the speed. All the while maintaining forward presssure on the radio. Lots of for/aft cyclic control.

Have heard some people in the US have reported makeing head stiffer so it will not flex will resolve this problem. Does any one else know anything about this?

Duane