iPhone 5, iOS 9.2.1 home button problems

After installing ios 9.2.1 on my iPhone 5 the home button is not working proper anymore.

When I open any app(3rd party but also apple) it needs several klicks on the home button to come back to the desktop sometimes.

The pressure point feels normal and there is no dirt or dust at the button.

I brought the iphone to a repair store. The technician opened the phone and checked everything. He said he is sure that there is no hardware problem, but a software problem, and I should reinstall the newest system software over DFU and iTunes.

So I did that, but after that clean reinstallation of IOS 9.2.1 it didn’t improve remarkable.

So my question is if that’s maybe a general problem of the first generation of iPhone 5(or others) with iOS 9.2.1 or is there anything wrong with the hardware, yet?

Any ideas?