IPad Air 2 screen orientation repeatedly frozen

Hi,

I have an iPad Air 2 64GB and lately the screen rotation keeps getting frozen. I have read the Apple support article "If the screen doesn't rotate on your iPhone, iPad, or iPod touch - Apple Support" and none of this helps:

- I know about the Screen Orientation Lock in the Status Bar and it is not set.

- IPad Air 2 does not have a side switch.

- The problem goes away after rebooting the iPad, but the problem comes back within a short time.

- I have backed up, erased everything, and restored the iPad. The problem is still there.

I first recognized the problem after installing iOS 8.4, but I'm not sure if it's correlated. It's very intermittent.

Now my questions:

- Is this a known issue, any known causes?

- Could this be a side effect of an app?

- Could this be a hardware failure, should I ask for warranty replacement?

- Any other way to diagnose this, are there other functions that also don't work if the orientation sensing is down?

Thanks,

Alex