I've created PNG's in three different programs, I've created them at 100x100 and 99x99 and 101x101. I've tried storing them to a cloud drive, my SSD, a NFS share, and a Raid 1+0 array. I even tried creating via RDP to a Windows Server in a data center. I've also tried taking a 100x100 transparent png from google for testing. No matter what I do. It just tells me the image is invalid.
My PNG's upload here on the forum fine. Somewhat annoying to see an image link not even work seconds after purchase, on the first settings page you have to go to to set it up.