iPod 6th generation blackout crashes

Almost a year ago, I bought a 6th generation iPod touch, which has largely been a huge improvement over my previous 4th generation one.

However, it has had maybe half a dozen "blackout crashes" from Sleep mode (screen stays dark), which I had imagined were due to faulty hardware. Although an in-warranty replacement would include the benefit of a new battery and shell, I hoped to keep this unit since I'd had the back personalized by Apple.

When it has plenty of remaining battery power, I've put it into Sleep mode, only to find that it won't turn on (Wake) when I pressed either of the two physical buttons. Up until a few weeks ago, my fix had been to charge it for a long time (e.g., overnight), then hope it turns on (Wakes) later, which did work but was frustrating.

Eventually I searched on the Internet and found the "Force restart iPod touch" solution, which worked for me and is in Apple's downloadable iPod touch (iOS 9.3) manual as well:

"hold down the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears."

Maybe I'd used this technique for earlier iPods, but if so, I hadn't remembered it.