Re: screws: my impression is that the screw(s) come loose from the plastic nut, the nut falls away so the screw now bears the weight unequally, tearing the hole in pannier material just enough to make the combo ineffectual. I now tighten the screws more regularly (and now know they do get loose) and put little metal backing plates on to help distribute the stresses on the screw.
As far as Ortlieb warranties, we bought them at MEC so swapping them was easy (props to MEC). Also, we are in the midst of our tour so when told about timeline to await developments from Ortlieb, we chalked it up to lessons learned.
ps My Arkels have been great
Just to repeat, I've owned ortiebs for just about 30 years, and haven't had any problems with mounting screws.
In the link to the Timothy towers problems, from the wear marks on his racks, it would very much appear that his setup+position of the two top mounts, and perhaps the lower tab, allows his panniers to move back and forth, causing the rub wear and the screw loosening.
My panniers don't move, the counter force created by the positioning of upper mounts and lower tab, in opposing positions, means there is no movement, therefore not rubbing or bouncing, so no wear and not vibrating loose screw.
To me, it's common sense to eliminate movement.
To be fair, ortlieb doesn't show clearly how to do this properly.
It's tricky, as each rack is different.
But I'm also think it's a Germanic thing, they think in a certain way and just assume everyone else does too.
If set up properly, your panniers should NOT shift, bounce, or move about over bumps.