Lines of Dead Pixels Across S2722

We've got 30 of these monitors, and some had singular dead pixels on arrival. 3 are now sometimes showing lines even when completely unplugged: intermittently on 2, constant even when powering on from black. The one with the worst issue/constant is about of the 3rd of the way up and horizontal, the others are vertical and closer to the sides. This worst monitor also cuts out at random, even changing plugs/cables. Support phone was completely unhelpful, and wanted photos from the test modes I'd already done, then wanted to connect at PC to test (the issue is apparent when nothing is connected, the line of pixels goes across the monitor menu), ignoring the fact we don't own any. Not sure our switch from Asus monitors was a good idea.