Mixed sources recording on mobile orders?

In a research wormhole earlier today, I stumbled on some online transactions that have a discount applied but no promotion in the usual sense.

I've got 4 examples where the Source at the top of the Order detail (I tend to look via the constituent record since I don't sell tickets myself) lists our generic Web source. One of these orders also lists the same source on the line item level; 3 have a different source, one that has a promotion attached and would trigger a discount. (Screenshots perhaps visible below?)

I've got an idea that there's something off with how mobile (TNMP web platform) is working with sources, but I want to understand what happens to let those two spots have different value. We found some old posts about seeing similar things, but no diagnosis. Anyone in 2019 have leads?