home button - contact problem

The home button on my iPhone 5 was damaged - rotating and no function. So i replaced the home button with a new one.

But the new button doesn't function too. Nothing when i press the button. So i ordered another home button (perhaps the first was faulty), but the same again.

I've measured the home buttons - all three have 19kohm when pressed. I've checked the contacts and the alignment, everythings looks fine. But stil no function.

While putting the frontcover back, i've noticed that the homebutton works on the last milimeter until the frontcover is fully closed / pressed down.

When i lift up the frontcover just a little bit, the homebutton works. Fully assembled / closed, no function.

Again, the contacts to the homebutton and the alignment of the contacts plates on the homebutton flexcable seem to be ok.

Can someone give me a tip for this problem?

Thanks

Marcus