Hello,
I have recently uploaded a shield that was denied because of transparency issues. So I whipped out Easy Gif Animator and reset the transparency and then re-saved the file. Just to be on the safe side I opened the shield up on GIMP and checked through each frame one by one and I saw no problems. So then again I uploaded the file and the little preview message on conformation of being uploaded had a black background, but I hoped that this black would not be visible as I presumed it was a pure color. After paying the 1000g and checking the code I went to wear it, however it did not exist. I put this down to me saying the wrong code, but after several attempts I knew that it wasn't working. I then patiently waited until the code emerged on TailorRichaards and on there it had the correct code yet there was no image, which lead me to believe something had gone wrong. Despite this I copied the code and tried it, but had no success and the graphic did not exist.
To cut a long story short, I rechecked all the frames and re-uploaded, but it was rejected again for transparency issues. After this I messaged Rufus to see if he could spot the issue, but he honestly did not know. I am not bothered about the 1000g, but I hope that a more experienced pixel artist could resolve my problem. There may be a simple fix that I have just missed.
Good Luck
note: searching for a resolution I exported all of the frames from Easy Gif Animator and compiled them on GIMP and only then did a black background appear on most of the frames.