Mostera adansonii: Mosaic virus or watering issues

[Magd3576]

So I brought home a monstera adansonii a couple of months ago and I noticed that the coloring was a little off--some parts are lighter green and others are darker. It's been putting out new leaves (about 1 every 2 weeks) and they don't look malformed but they do have some lighter coloring again. Of course, I started googling and I keep coming across the mosaic virus, which does occasionally, but rarely, affect this plant. However, the other options were the usual lighting/watering/humidity combo or under fertilizing or pests. A couple of days ago one of the older leaves started to yellow. Normally this wouldn't worry me, but the yellowing seems to have dark veins and I don't know if this is normal for the plant or a sign that it needs to be removed. I have some fungus gnats but I haven't seen anything more sinister than that (but I am paranoid about thrips). For the time being, I have quarantined the plant in another room without any other plants.

Sorry, these photos aren't very clear (and my leaves need a wiping down) but the yellowing leaf (first photo) has the most distinct color differences. The other leaves have some lighter spots (like near my thumb in the bottom photo) where it's harder to capture the color differentiation but it occurs fairly subtly across most of the leaves. I also know we can't confirm mosaic viruses without lab testing, but I'd rather not throw it out if the problem is just that I haven't figured out its water/light needs. Thanks for your help!