Walking the subfloor seams first is smart, I used to skip that thinking it was a waste, but not anymore.

Oh man that brings back bad memories. My buddy ran into this same thing in a rental down in Gresham, guy had used 3 inch roofing nails and shot them right through the strip and pad because the concrete was too crumbly to hold anything else. He tried to just fix the visible ripple but once he pulled the carpet back he found the whole wall was done that way, strip was basically hanging in the air. He ended up having to pull the whole room, grind down the old nail heads and glue fresh strip with a good construction adhesive, cost the owner way more than the first guy saved. I'd say if you only found 8 feet of bad strip and the rest is holding, patch it and move on, but warn the manager that if the ripples show up somewhere else you're doing the whole thing next time.