hmmm...where could I find this info. Maybe I will pull up Priority Pass website and read the FAQ's...bam in 20 seconds I found an answer

"Why have I been denied access to a lounge on the Priority Pass program?

We apologize for the inconvenience. Sometimes lounge operators will impose restrictions based on lounge capacity, to ensure guests have a pleasant experience."

I have been denied at ORD T5 before, but went back an hour later after a couple flights departed and was allowed in.