Found a solution
I had a the exact same problem, and luckily I found a solution just in the moment I had already decided to factory reset.
I have the stock rom/bootloader/etc installed, no root.
Well anyway, factory resetting the phone is not an easy task either, so this is what I did to get to the factory reset option in the boot loader:
I pressed power for a loooong time, then the phone shutdown, I pressed power and vol-down for a looong time.
Some kind of boot menu appeared, I chose recovery.
At first I was stuck with a red triangle with an "!" over a lieing android. I found that pressing and holding power for 1 second then, while still pressing power, pressing "vol up" for 1 second and releasing both at once, presented me a special menu, wich contains the factory reset and option ... and also a mysterious "wipe cache" option, which sparked an idea of how I might circumvent the factory reset...
I remebered, that after the last OTA update the phone was so busy after reboot, that the NFC Unlock app was loaded after a long delay, while I was already able to interact with the phone.
So I though what the heck, before factory resetting the device I might as will try wiping that damn cache and see wether that caused the delay.
After wiping the cache, I booted and Android went through all those apps, and then showed the launcher/home screen without the widgets loaded etc, for just long enough to switch off the airplane mode, before the unlock app was loaded and immediately locked the screen again.
It might have helped that I disabled the SIM Card PIN check, i don't know.
Only this time I could unlock it normally
I hope this helps