Heavy deadlifts, loaded carries, and weighted spinal flexion are the usual suspects when a lower back is irritated. RepRoute's response is deliberately simple: it stops programming them.
Flag the lower back and every exercise carrying the lower_back tag is REMOVED from your plan. In the catalogue that tag sits on every hip-hinge (all deadlift and RDL variants), every loaded carry, and every core pattern — flexion, anti-extension and anti-rotation alike. So planks and Pallof presses go too, not just the sit-ups. It's a coarse cut, and it errs toward taking too much rather than too little.
Days emptied by that strip get refilled with up to three exercises from the patterns still available — squats, presses, rows. Your leg day doesn't vanish; it stops hinging.
One thing RepRoute does NOT do: reduce the load or shorten the range of motion on a movement before removing it. There is no half-measure in the engine. It's either in your plan or it isn't. If you want a gentler adjustment than that, use Swap during the session on the specific movement that bothers you.