iPhone showing connected to power but still not charging

I manage iPhones for a small company and I've seen this problem on iPhone 5s, 6, and 6s since November 2015 when one of the IOS 9 updates came out. When attempting to charge the device, the phone confirms it is connected to power (the lightning bolt appears next to the battery icon, the power connected tone/vibrate sounds), yet it does not charge and the battery continues to quickly lose power. Note, this is NOT an issue with the phone not recognizing it is connected to power, there are plenty of discussions about that and this isn't the case - it confirms power is properly connected!

When this does occur (lately for me personally, about twice per week), nothing will enable it to take a charge. I've tried different cables, power adapters (yes, all of them Apple certified), hard reset on the device, and cleaning the lightning port. I also regularly close out all running apps and charge in airplane mode, no help. The only thing to do is let the battery completely fail to 0%, reconnect power, and after the device restarts it will finally take a charge and behave normally for a few days. Eventually, I'll notice that the battery is losing its charge more quickly than normal even though the phone is idle with no apps running, and that signals this cycle is starting all over again.

I've seen this happen on a 6s and a 6 Plus within a week of them coming out of the box, and two 5s phones. Is no one else experiencing this?