This may be of help:

I too have been rejected for the past month every time I tried to use the Pre-Check line. After talking to a TSA official at the airport (who told me to contact Delta) and talking to a Delta support person (who told me to sign up for Global Entry, but I'd rather not pay $100), I finally found a Delta support person who was knowledgeable about what's probably happening to me.

Recently TSA started insisting that Delta's Secure Flight Info record matches EXACTLY with government IDs.

In my secure flight info in my Delta online profile, my middle name is blank. But my government IDs (driver's license and passport) display my full middle name.

The Delta support person said that this will cause me to be rejected at Pre-Check.

On Delta.com, it isn't possible to edit one's middle name. So I called Delta's web support at 888-750-3284 and they entered it for me. Then she had me select "Edit", uncheck the "Save my Secure Flight Passenger Data" box, then RE-CHECK the box, and then press Save Changes. (Just to be safe so that the system knows I made a change.) She also re-sent the info to TSA at her end, she said.

She was not able to edit my middle name in my basic Delta Skymiles record, though. To get this done, I had to fax a copy of my driver's license to 404-773-1945 and request them to add my middle name to my record so as to match my government IDs. (I just did this today, so it will probably take a few days to get done.)

Theoretically, I should be fine now. She says it doesn't matter if Delta is showing my middle name on my boarding pass because the boarding pass has a barcode that includes my TSA Secure Flight Information name. But I'll still be nervous until my Delta name record exactly matches my Secure Flight Information name record.

Wish me luck. I'll post my Pre-Check success (or lack thereof) after my next flight. But I wanted to post this information right away in case anyone else is in the same situation.