TL;DR: My wife's LG Nexus 5X has no issue charging with her LG charger or my Huawei charger. My Huawei Nexus 6P charges slowly with the Huawei charger but at full speed with the LG charger. Is there an explanation for this, and am I likely to run into more incompatibility (i.e. is it my phone or the charger)?
I have a Huawei Nexus 6P, and my wife has the LG Nexus 5X. When we first received them, we could use both either charger/cord combination and we would get the full 3A/5V ("charging rapidly" message appeared).
After a month or so, I noticed that my phone wasn't charging as quickly as I was used to, so I looked and saw it said "charging" but not "charging rapidly," which is what I get when I use a regular 2.1A charger. I looked and this was on the stock Huawei charger (that went with my 6P). I tested this setup with my wife's phone, and her phone said "charging rapidly."
At this point, I used her LG charger, and I once again got the "charging rapidly" message. I then tried both cables in both chargers, and it was only the original cable with the original charger that gave me a slow charge (charger and cable from Huawei). I did the experiment back-and-forth several times to make sure it wasn't just a fluke.
That was fine, I just switched the cables and was able to use either charger and get the "charging rapidly" message.
Eventually, though, I noticed the issue again, but this time with the cable from LG and the charger from Huawei. I tried switching the cables, but it didn't work.
So now my Huawei phone can't charge at full speed with the Huawei charger, but my wife's LG Nexus 5X can without issue. My 6P can charge at full speed with either cable using the 5X charger, but won't charge at full speed on the 6P charger with either cable. The 5X can charge at full speed using either charger with either cable.
I realize that I could just pitch the charger and maybe never have to think about it again, but that doesn't make any sense out the problem. I'm curious about the very specific progressive incompatibility, and I also don't want to deal with the same problem with another charger or set of chargers down the road.
So, is there any explanation for this hardware incompatibility? Also, is there a good chance this is a software issue? I noticed it after flashing either PureNexus or Chroma, but I'm sure it carried over after going back to PureNexus from Chroma, so I'm assuming it wouldn't be fixed by going back to the stock ROM.