Why isn't my Nexus 4 Pin working?

I've had the same pin for the past two years. It suddenly stopped working tonight - no idea why. I tried logging into my google account to reset it - didn't work. Any idea how to unlock it without doing a factory reset? I don't want to lose all my pics and writing. Also, any idea how this could happen??? Thanks!

Ps.
It's not a 4.4 or lower.

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