The overall mottling - which I think is what you mean by "swampy background" - was another trait of the ink transfer. It ruined entire films and was why I gave up on Shanghai GP3 altogether in the end.
I actually went back to the 220 roll I mentioned earlier in this thread and re-digitised it with a better/more polished setup. In doing so I noticed some odd streaking - not consistent with development artefacts, as it was running the wrong way across the frame - and an odd "rash" across certain frames.
Here's the whole frame, unedited:
View attachment 4859598
And here's a tight crop of one of the affected areas:
View attachment 4859600
I checked the negatives - tiny pinholes everywhere. Apparently it's a common problem with this stuff.
Really frustrating, as Shanghai are basically the only game in town for these neglected formats. I hope they can get the QC issues dialled in for future runs.