TL;DR at bottom.
I've bought a new kitten 2 weeks ago. I had her confined to a room the first few days, with litter box and food/water. After a few days, I've let her roam the whole apartment, and moved the litter box to a new location (where my other cat's litter box is). That didn't seem to bother her, and she used it regularly.
Now, she has had diarrhea for the past 2 days, and while still using her box, she also started pooping at places other than her litter box (on the bed, bathroom, etc.) At first I thought it was because of the diarrhea and that she just didn't have the time to go to the box. However, earlier I was observing her, and saw her jump down from the cat tree, walk into the bathroom and take a poop there on the floor. So she is doing it intentionally. Also, her diarrhea is better and while still a bit soft, her stool has a "form" again, rather than just being a puddle.
Why is that? Why is she suddenly not using her litter box anymore? I didn't change anything in the last few days, so I'm quite confused. The only thing that comes to mind → I've used some lightly scented (aloe vera scented) wet wipes, to clean her litter box, as she got poop all over it while having diarrhea. I'm pretty sure she used the litter box once or twice, even after I've cleaned.
Some information about the litter box.
It's a closed litter box with a swing door. It's quite big, she definitely has enough room in it. I clean it daily. I use pellets made from plants. She also has access to the other cat's litter box, which uses a fine grain litter also made from plants (I think it's corn). She sometimes used it in the past. My apartment isn't huge, so the litter boxes are next to the washing machine/tumbler. That being said, I've never seen her be particularly scared of the noise they made, and they might run at most 1 time a day.
TL;DR: New kitten suddenly stopped using litter box since having had diarrhea. Her stool is back to normal, but she still is not using the litter box, and intentionally goes somewhere else to poop.
Any help is appreciated.