oh thanks:) I just registered here yesterday, still have to figure everything out! For example what artifacts means...
You seem to be having problems in your file outputs. This too has artifacts and color count is over 250.
Update art using the 'edit it' undr the art and hit submit again.
Use the forum if you need help :)
Artifacts is just extra data in a file that in pixelart changes the pixels. You did not pick over 250 colors manually so this file was saved oddly. I hope your original file did not get messed up :/
Use the forum if you need further help.