Several issues were listed as possible problems with my vector files. I think this might be the relevant one: "Your JPEG preview resolution must not be less than 5,000 X 3,000 (15 million pixels)".
I resaved one file that I think solves the problem. I have very many such files and I want to know if this fix works before reworking and resubmitting. Here is a file to check.
Your file is much too small. What I do is to make my vectors 4000 X 4000 pix, submit that and allow Adobe to generate the JPG for the thumbnail. However, I do not submit many vectors at a time.
Your artwork looks to be too small:
Adobe uses this value to generate the JPEG and PNG files.