Has anybody experienced the model paint fading away due to exposure to direct or indirect sun light in a glass model cabinet?

I have not experienced this; however, this is a common issue with most products with paints and plastics not designed for UV protection. I would suggest a different storage method, or somehow protecting the glass through a window film that blocks ultra violet light. It's quite amazing how much simple sunlight can degrade and how quickly.

What do you mean you don't store them deep in your undergound lair?

Sunlight does tend to damage models over like 10-20 years in direct light, but at worst the paint will just lighten. This is more of a problem with Legos, because it also damages the part connections. However, this game has been out for like 4 years so your models shouldn't be too damaged.

Do you happen to live at an extremely high altitude?

Ion burns and running through Conner nets can fade the paint, dark matter also puts a stained tint on the leading edges.

It's generally a good idea to keep anything you value or want to display away from any direct (Possibly indirect, too) sunlight, for this exact reason. It doesn't take 10-20 years for color to fade, in fact it can occur over the course of 1 year depending on the pigments used.

I have several paintings, and replaced all the frames' glass with UV resistant ones after discovering fade on one of them.

Yeah, house siding which is made for uv resistance fades quite a bit over 10-15 years.

I have dozens of models from FFG and GW that I have painted over the years and none of them ever see direct sunlight, even in the game room which is on the northside of the house. I've spent a lot of time painting, I'm not going to let the sun and its ultra stupid radiation ruin my ****.

What is this "sun lite" you speak of?

What is this "sun lite" you speak of?

No idea, my war room is black-curtained off...