Log-in screen does not log me in,times out and asks for password again

Hi all, my first post here :)

10 Pro, 1607.14393.105 on C: SSD, data and user profiles on E: hard drive.

While I am one of the rare people which seemingly had no problems with initial build 1607 Anniversary Update, as of the first quick patch for it (KB3176938 on 01/09/2016), login screen has stopped working - BUT ONLY SOMETIMES! I didn't work out any patterns.

First noticed this last Friday, just one day after the KB3176938. Windows boots up fine, login screen, put when I enter a password, the circle keeps circling with "Logging in" message, SSD light goes flashing for the first 10-15 seconds, but after a rather long time (40-50 seconds?) it goes nowhere and just gets me back to the welcome screen - with clock, which once you press a key displays a login prompt for password again. I remove clock, try to log in again - same. No matter how many times I tried. I shut down, boot up again, try to log in, lets me in.

Next day - same thing. It was very consistent - first boot-up login goes nowhere (even on empty password - not warning me "wrong password" or anything), shut down, seconds boot-up lets me in.

But then on Sunday and Monday I had to shut down twice before letting me in. This was already annoying, but today, I had to do it 5 times at least!

Absolutely nothing got installed on the PC in the last 7 days, nor I changed any configuration. I disabled recently Fast Boot, but this was about 10 days ago or so.

As a short term solution I disabled user login and login screen, now boots up straight into Windows and (on only one boot-up so far) works fine. But I'd rather fix the issue if possible.

Any clues or suggestions? Has this sort of behaviour been documented anywhere




P.S. Not sure if it matters, but may be some clue. Out of my graphics adapter (GTX 970), one HDMI cable goes to the TV, and one miniDP cable goes to the PC monitor. Due to internal in-built priority on graphics adapter, this means that before Windows boots up, the BIOS screen and Windows loading screen gets shown on the TV first, and only on Windows login screen the PC monitor gets the picture. Ever since this started happenning, the SECOND BOOT UP OF THE DAY goes to the TV, does not go to PC monitor any more. Once logged in, the PC monitor does indeed get the feed from the PC. This has never happenned before in 11 months of using Win 10, or for 10 years of using Windows 7 with the exact same setup.

OK, when I posted this question it was in "General support" where I found nothing similar, but since mods moved it here, I actually found no less than 3 similar topics.

I forgot to mention last time that this was to do with a local account, not the microsoft account. I only sign in with a local account.

After updating to 1607 Cant login to windows with my password
(only solution suggested - fresh install and no 1607 update - this is a bit drastic, surely there is something else to be done, and also, 1607 fixed one glitch that was making my life hell, I like 1607)

Only able to login after I restart 1 time
(no solution)

Can't sign in after the Anniversary update
(no solution)

If there's no workaround right now that's fine, I'd just like to know if anyone knows if this problem has been documented with Microsoft and is being worked on, as being able to log into one's PC is, well, fairly important to the general usage of that PC?