I tried a test upload a bit ago and had no issue. Maybe one of the server staff was testing something (and mistakenly did so on a production server).

If not that though, what was the size/format of the source image?

the size of the pictures I post are usually 800x900 ~ 900x600 anything in between
it's just ruining the quality for some reason and I'm noticing it with another artists works as well :(

Okay, I missed the part about it looking pixelated.

If I had to guess, it's probably a bug in the image processing software they use. I don't know what they're using now, though. They used to use ImageMagick, but then the "ImageTragick" exploit happened and they either had to change to something else or update the server code with countermeasures (not sure which).

ooh, that makes sense D:
Hope they can fix it soon, it's sad that a website for uploading pictures is messing with picture quality xD