There is no guarantee to get the TSAPRE record onto your boarding pass. - As they might exercise their discretion of not granting it to you for that very specific flight.

You'd have to ensure that date of birth as well as your name is exactly what TSA knows about you.
Keep in mind: in some forms LX is using the european date format (DD.MM.YYYY). - If the date of birth doesn't match, TSApre won't show up.

Generally TSApre works with LX (but the LH/LX form to key it in (and have it stick to the booking), is sometimes a little bit challenging).

If it does not appear on your boarding pass:
- double check that you keyed in the date of birth the right way
- approach a check-in agent and let them double-check it / remove the KTN and add it back on again
- if it still doesn't work, you'd have to reach out to the TSA within 20(?) hours or so to have them check it.