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Did a batch of 17 .jpg files, all uploaded fine. Try to upload a .png, seems to fail if the file size is above a certain size. Uploaded some png's that were 2.09 MB or less, uploaded fine. Tried one at 7.54 MB, fails every time (stuck at 100%).
Customer support service by UserEcho
Stuck at 100% just happened with a 6 MB jpg as well.