I can't say 100%, and full caution etc that if it's bulging that has to do with casing failure/damage or installation error then you should stop riding it, but it sounds like it's probably distortion caused by imperfections at the casing seam. Marathons, for everything nice about them, are a little notorious for this. Schwalbe will generally warranty particularly bad ones, which if you can feel it clearly while riding I would say these are. At times I've seen a lot of them that needed to be sent back for reasons much like you describe, suggesting a QC step getting missed or a machine not working right or the like. As the incidence of the problem has seemed high during certain time periods, it doesn't strike me as unusual to have two tires with it, and in fact that both tires have the issue suggests it's the seam rather than casing damage.
You can usually confirm that it's happening at the seam by examining the tire to see the look of the fabric layer under the rubber, or inside if you have the tire off, then following around to where you see that pattern disrupted, stacked double for a small bit, etc.
I've speculated that the kind of left-to-right diagonal distortion you describe is caused by something along the lines of the cuts of material not being square or the seams not putting them in a square orientation.
Riding the tires like this won't typically hurt anything except perhaps your enjoyment and steering control. It won't affect the tube, rim, hub, etc. Also, the distortion by itself from messy seams usually doesn't imply any inability of the casing to constrain the tube. If you're using rim brakes then you'd want to make sure the distortion isn't causing rub between the tire and pads or brake arms. And you also want to make sure the bulge isn't causing that spot to get close enough to the frame/fork to cause rubbing or clearance too tight to allow for some debris build up.