[toomuchcoffee]

I pressed further, and they informed me that she could not be let in because she was an "undisclosed security risk."

Y'know, it might just be some poorly-paid security drone reading blindly from some poorly articulated status message on some crappy security desk app.

So instead of something tactful and polite like "Not on the guest list", the applicable field got set to NULL, which bubbled up as "Reason: Unknown".