It does look uniform, like something went wrong.
Did you use soft scrub or a spray of bleach cleaner to try and remove it though?

Ugh, so sorry you're having stain issues.

DXV is the rebranded name of Porcher. The company was sold to American Standard last year, production was suspended for a time (at least for tubs) and they are back in production under the new name of DXV. I've no idea if there were other changes to the line other than the name but you might have more luck searching for reviews under Porcher.

My tub is a Porcher, the last model and a floor model to boot, that I could find anywhere after the business was sold. At the time, the plumbing rep wasn't sure what models would be available after the dust settled. The tubs have a good rep and I would assume their other products did, too, but I don't know that for sure.