I fly nearly weekly, almost entirely domestic (USA) and have cleared Precheck many hundreds of times. Recently on a departure from BOS to ORD the TSA agent scanned my driver license as usual, then asked for a second form of ID. I know FL licenses sometimes are hard to scan so I asked "Is my license not scanning?" and was told it did scan properly, but the screen instructed him to ask for a second form of ID. He could not give me a reason, just that the computer told him to ask for it. I've cleared security with that very same license hundreds of times with no issue. License expiration is 4 years out so it's not like it's about to expire.

Any idea why a second ID would have been requested? I always keep my passport with me in a separate bag in case I lose my wallet so no big deal, but it's kept me scratching my head since.