I've had it happen twice. Precheck didn't appear and I called Delta and the number for some reason wasn't in that reservation even though it wa sin my profile and the agent unchecked me and added it and when I check back in it was there.
Also make sure your name is identical in your delta profile to what is it on your trusted traveler number. I didn't get it precheck the first time after obtaining my trusted traveler number (I have precheck only not GE) and found out it was because when I applied for precheck they used my full middle name off the passport and Delta only had my middle initial. Delta unchecked me in and added the full middle name and then it appeared.