I ran into that a couple of weeks ago as well (that checkpoint is "Checkpoint 1"). Checkpoint 4 is also solely for Precheck (and Clear) and it is always open*, although a bit of a walk from CP1. It's closer to C/D gates but as LIH Prem says, everything is connected once airside so it doesn't matter all that much save for the walk.
* - SeaTac website says open 4am to 11pm. but those are the max hours shown for any of the checkpoints. Not sure if they close at 11/open at 4 when some of the Asia flights depart after 2am and the first flight bank of the day is at 5am.
Last edited by flatdawgs; Jun 18, 2019 at 5:35 pm
Reason: typo