Do you water with tap water? Some plants are sensitive to chlorine. I don't know much about this variety, but my peace lily hates my city's tap water. Chemicals in tap water can cause browning on leaf edges of some plants. I'll let the experts weigh in.

Is it a leaf or a plant, monster con be propagated by leaf cuttings?!?!

Whatever the case, the leaf is dying and will not grow back.

Monstera deliciosas aren't sensitive to tap water. I've watered mine with it and never encountered any problems. Do you give your cutting plenty of sunlight? I would give it as much bright in-direct sunlight as possible. Plants need to photosynthesize in order to produce the food they need to grow. And they can't do that without sufficient light.

Does the cutting contain a section of the stem containing one or more leaf nodes?

Almost looks how a plant does during a spider mite infestation :(

Thanks for your comments. It does have a leaf node - and a pretty large root structure (that I saw when I first replanted it). I've tried to keep it out of direct light - but maybe I'll try another location...

I wouldn't recommend placing it in direct sunlight, just one with brighter indirect sunlight. Maybe in a spot that's warmer as well. If it's already got some roots, that's a good sign. Just give it some time, and make sure the soil doesn't dry out. Do you see any new growth? Other than roots?

These are tropical plants that love warm humid environments. When I had mine inside over the winter months, it still grew. Just at a slower pace. But once I placed it back outdoors for the summer, it started growing much faster.

If that stem was recently cut from the parent plant then the loss of the leaf isn't unusual. But there should be signs of a new growth emerging from the stem. Check the stem and roots for signs of rot.

I would cut that leaf down by half, following the natural shape of the leaf.

I would give the leaf portion a shower every day in case it's bugs. Have you allowed the soil to dry too much between waterings? What size is that clay pot that it's in? Can you take pictures of it from different angles including the pot and inside the pot?

Edit: I'm going to take a picture of what I mean when cutting.

This is Philodendron hederaceum. I cut leaves sometimes when propagating vines if it looks like the leafs are transpiring too much and causing it to be unable to root. (Sign of this is when the leaves are constantly wilted)

What ever happened to your monstera?

Here's mine. That's not it.