Pretty annoyed because my Anker Powerline cable won’t charge my XS over 80%. It worked on the 6S, so I don’t know the problem is. The stock cable works, so I have to use that for now.
With the modern battery meters needing calibration (100% changes as your battery ages), it was likely charging just fine, it's likely that the value of "80%" was changing. This is why i charge my phone a couple hours over 100% the first time or two and let it wear out to the point of shutting off.
In other words, what you're seeing is not abnormal for a first charge, just something you won't usually notice.