This happened to me last year. Probably 4-5 times in a row ex-DTW before reappearing for DTW-AMS and disappearing again for another several trips ex-DTW/ORD/LGA/JFK. The real hassle was the behavior of TSOs, never mind the line, at the non-PreCheck lane at JFK. (Also I'd been receiving X on my GE slips consistently for over one year)
PreCheck designation reappeared on all my boarding passes so far in 2018 with no issues, and GE finally worked properly for the first time few weeks ago at JFK.