Hello, and welcome!
The TSA Precheck or any other program for which you applied, that issued your KTN, is a random selection process for all flights. Even though you've been selected to receive it on your two most recent flights, unfortunately, this time, you did not. Here is more information for you to read about why you will not receive Precheck every time you fly:
"If you check-in online before your flight and don’t see a TSA Precheck indicator on your boarding pass, contact your airline or check your airline accounts online to ensure that your Secure Flight information is updated right away. If you have flights with multiple TSA Precheck-participating carriers, ensure that your KTN is listed with each individual carrier, as they submit this data to the TSA for TSA Precheck verification starting 72 hours prior to departure.
If everything matches, you’ll be able to re-print your boarding pass again, hopefully with TSA Precheck this time!"
Make sure that you register your KTN number with all the airlines on which you are a frequent flyer. Also, make sure that you provide the KTN information when the reservation is made. Reservations made before you received your KTN will not reflect that expedited screening service on your boarding pass, however, you could call your airline and see if it can be changed for tomorrow's flight, even though it's not 72 hrs. in advance.
I hope this helped and wish you safe travel!
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