BTW, I have used the "angled finger" as Apple shows in their example. something that always failed within a few hours for me, and while it worked initially, and still does for my primary thumb, I just checked my other thumb and the angled tip is not working.
Update: creeping up on the failed angled tip to "retrain" the failed angled thumb brought it back. Not done from the fingerprint add screen; Just using the sleep/wake button with small movements on the home button starting from a working area and moving towards the tip, and finally to an angled tip. Took about 10 cycles, maybe about 15 seconds or so. Hardly jumping through hoops...
An old observation seems to still be true, that is, use it or lose it. Will try alternating through all fingers over time and not just my primary.
I really believe this is not a function so much of how the prints are registered, though that might help/hurt a bit, but it appears that it's really how the Iphone updates or "learns" or corrupts the prints over time. Otherwise people would start having problems immediately, and that's not the case from what I've experience and read.
For example I can register my index and thumb on both hands and right after doing it, they all work perfect the first time, no issues, all different orientations, etc. However, 3 days later 3 of the 4 no longer work. One thing I've noticed is that I use my right index finger the most, and it always works longer than the others. That almost suggests to me that for some reason over time even if you don't use say your left thumb the software corrupts the registered print, the fingers you use more often are more likely to be "updated" or modified correctly. It's also possible that the print recognition is just too "touchy" and for users who's prints change more than others the software just refused to recognise them anymore, and perhaps isn't learning enough on frequently used prints.
This might also indicate that even if you don't use a particular finger the software is degrading/modifing the print over time, which may also mean that if you only register the finger you use most it might last longer (though someone has probably tried this).
It makes me wonder that if you unlock the phone a few times a day with every finger you register if it will do a better job of not corrupting the prints over time.
One thing I've noticed is that the hand soap that I use seems to have something to do with it. TID would only work if I'd wipe the sensor before, and I thought it was a faulty sensor. I enrolled someone else's fingerprint, and it worked no problem. I have a lotion type hand soap, but after I switched to a regular bar soap, it seems to work better.
I have the same problem. Works great initially then recognition gradually gets worse until less than 24 hours later it does not work at all. iPhone 6 Plus purchased less than a month ago. Have also tried all of the workarounds - wipe reinstall, reset, multiple copies of the same finger. That did bring to light that the decay of recognition is per print. Each one decays at the same rate from the time it was entered. So the first one entered stops working but the second one lasts another couple of hours. This is even for two copies of the same finger.
If there IS a physical characteristic that makes some people unable to use TouchID, then why not publicize it so that they are not purchasing a phone to get Touch ID and Apple Pay and THEN finding out that it does not work? Couldn't Apple stores have sensors in them that you could try, to determine if you can use Touch ID? Do a search on Touch ID in Apple's forums. There are hundreds of messages about problems. I wish this issue had gotten more exposure before I purchased my phone.