The wipers in the 1972 stock are leaving a trail of faint wipers behind them as they wipe. I’m driving the A Round Haul scenario which is in the rain. The rain isn’t really appearing on the screen either, so despite it raining the screen isn’t getting wet at all with no droplets of water present.
If you have motion blur turned on it will leave faint wipers behind. It's really quite broken but it's a known issue with motion blur. On that scenario it was weird, I had pretty much no rain going towards Harrow & Wealdstone but had considerably more going back to Queens Park. Presumably this is to do with wind? But I don't know, it's off either way (PC player).
I know motion blur doesn’t do this on trains in TSW2020. The rain on the screen is present on my return journey too. EDIT - The wiper trails are there without motion blur, so its not that.
I'm also experiencing this, and it's quite annoying. The wipers also seem far,far too loud in my opinion.