Touch id iPad 2 works intermittently

My iPad air 2 touch id started working intermittently a year ago: it suddenly died, which means that is is not sensitive to ANY fingerprint (while the regular press-home function still work); tried all the standard procedures including all kind of reset of the iPad with no luck. So I just disabled fingerprint access (Apple Genius told me that the touch id cannot be replaced since it comes together with the motherboard and being out of warranty I just decided not to pay for an iPad replacement).

One month ago just for curiosity I tried to turn on again "touch id an passcode" and to my great surprise it started working again.... flawlessly until yesterday, when it died again.

My first guess was (and still is) a hardware issue, but this intermittent behaviour makes me not 100% sure.

Anyone with similar problems?

Thanks a lot

Sami