I hope that seed is indeed fresh, problem is one never knows. Both Steph and I had problems with germination of OGC lettuce this spring, when normally they are reliable.
Anyway I suspect it is more the season, your sowing was a little early and land cress seed I think likes a cooler night or two before it germinates, as it “wants” to grow in the winter months rather than midsummer, so I would keep the tray cooler.
