Is the little screw on the back that attached the unit to the headstock tight and flush with the baseplate? It could be the tuner itself could be getting caught on the screw if it's sticking out, even a little bit.
I realised this when I installed mine, I thought I could use the screw from the stock tuner so that it wouldn't cut a new thread in the hole, but it was a dome topped screw and the hipshot wouldn't swivel over it.
Also, the instruction manual says they are supposed to be lubricated every now and then with vaseline or lubricant grease. WD40
AFAIK in more an instant fix lubricant, designed to unclog but lubricate in the long term. I haven't done mine yet in the six months I've had it, but it might be worth it.