Hello, and thanks for your patience.
I see you had asked your question quite a while ago. Different experts are online at various times and I recently logged in and read your question.
When you submitted to a TSA background check a few years ago, were you approved and issued a TSA Precheck number or 'KTN' (Known Traveler Number) or a different kind of approval for a GOES (Global Entry) or SENTRI card, also, with it's own number?
If the answer is 'yes,' you might not have been selected to participate in going through the fast screening lanes just due to the randomization of the system. All passengers who have TSA Precheck or another fasttracking card/number are not guaranteed to receive the service on every flight. This is to further enhance security measures.
It's recommended to let all the airlines you fly frequently, know that you have TSA Precheck and add it to your profiles. This may help you get chosen more often to receive the advantage when you fly.
However, since you mentioned you had the background check done a few years ago, if it was more than 5 years ago, TSA Precheck and GOES are only good for 5 years and then you have to renew, so you might want to look into that, if the time element matches.
I hope this helps, but if you have additional questions, please click "Reply to Expert" or "Continue Conversation" BEFORE rating. If not, please rate positively, so I receive credit for my assistance, otherwise, I will not receive credit. Thank you!