Solved and/or "Try this" - DST6501 won't pair with the software WPS button

This is a two part "solved/maybe" post in case it helps anyone. I'll post the other topic separately also, but cross reference the two: Router, Nighthawk R7300, firmware = V1.0.0.74_1.0.29, DST = DST6501, firmware = V1.0.1.6.

Problem: DST6501 won't pair up with the router when you use the web based WPS wizard: 

This might help: On the router, try the hardware WPS button (read manual, it's there), not the web interface WPS button. 

I had successfully paired the two a few days earlier, no big deal, but I was working on my other problem, where the extender was actually using WPA2+TKIP, even though the User interface clearly was set to WPA2/AES.  I decided to try setup from scratch, so I reset the extender to factory settings with a paper clip, and tried to pair and start over.  After at least 15 tries, probably more like 20, the thing just wouldn't pair.  For all those 15 or 20 tries, I was using the WPS Wizard (Advanced, WPS Wizard), which for all intents and purposes, gave the impression that it was trying to pair (but without ever succeeding.) I did all the usual things, moved to closer electrical outlets, tried the PIN, everything I could think of. 

Eventually, when I just used the button on the router, it paired on the first try. (On the R7300, it's the second LED from the right.  It looks like an LED indicator, but it's actually a button.)

Maybe it was coincidence and the extender and router would have paired on the sixteenth try anyway?  I don't know, I'll just say the WPS button on the router itself paired on the first try. So, give it a shot if you have trouble.  Good luck, maybe this'll save an entire wasted Sunday morning for someone else.

P.S.  I'll create a separate thread; but short version, if the UI says WPA2/AES but your iphone still warns about weak security (and your Wifi Analyzer shows the network as using WPA+TKIP), try this: Click the REBOOT button in the Extender's web interface.   (Changing security to NONE then back to WPA2/AES didn't work for me, and unplugging replugging also didn't work.  The REBOOT button on the web interface did.)