I don't know if this is a bug or not, so I'm sorry if this is in the wrong spot. But I know that myself and other artists on HEE have been having issues with uploading horse avatars. We get the "Image must be under 100,000" error message, even though the file is well under 100k. (Like 90 or so.) We are resizing, exporting, linking, etc. the same way we always have, and never had trouble like this until the past month or two.

I am having the same trouble!

Not having these issues, neither is Kiber

I've had these issues in the past few weeks as well.

I´m not an arting person - but as much as I know from electric devices, not every program and every PC/laptop/phone etc. saves the datas from a pic in the same way.
Some save kind of additional datas in the background that makes the art file larger, even if it says that it is sized within the right range.

This is why it might happen that you will save your art in 500x500 with 95k and when you want to upload it. you will get the message that it is oversized.

Only chances you have is either save/resize it with another program in the future or you use good old paint for resizing and make your art smaller pixel for pixel until you can upload it.
But dont forget to set the checkbox for "keep the proportions"