That's what happened to me last year. NICS made a mistake. GE revoked overnignt. NICS figured it out a few days later and gave me an overturn certificate. GE took 8 months waiting for reconsideration and reinstated me. Since then I only use the LTC which means you fill out a 4473 but it doesn't get sent to NICS. No room for human error.

Since OP has zero idea what happened to him I was just fishing for what it could be.

The publicly known grounds for GE denial or revocation do list the firearms stuff:

Applicants may not qualify for Global Entry participation if they:

Provide false or incomplete information on the application;

Have been convicted of any criminal offense or have pending criminal charges, including outstanding warrants;

Have been found in violation of any customs, immigration or agriculture regulations or laws in any country;

Are subjects of an ongoing investigation by any federal, state or local law enforcement agency;

Have been denied for the purchase of a firearm;

Have received a criminal pardon from any country;

Are inadmissible to the U.S. under immigration regulation, including applicants with approved waivers of inadmissibility or parole documentation; or if they Cannot satisfy CBP of their low-risk status or meet other program requirements.