I have exactly the same setup as you and I feel the same about it. It wanders everywhere. Feels unstable at high speeds and under braking. The back also squats down under hard acceleration and makes the front end light. I also find that if I let the car roll forward a little bit from a standstill and then come to a stop again - it bounces momentarily and takes a while to settle.It feels great round low speed corners, it turns in and just grips but high speed bends and even in a straight line the car feels very floaty, it weaves about a fair bit and to be honest it's not nice at all.
Braking from high speed the car is all over the place, it's scares me sometimes not gonna lie haha.
I thought it was just me but clearly not if you're also finding the same. It's bothering me so much that I considered putting it back to stock or trying a Bilstein B16 kit or KW V3.
Is it because of the damping or maybe the spring rates being different from standard? Maybe someone with more knowledge will know.