I noticed, in the settings for UpdraftPlus, I didn't check the box to delete the local backup. So I did that, and and tried again. The files in my S3 bucket were actually there, and I could download them, but not all of the files were there, but they were all on my ftp (and none were deleted).
I've done this multiple times, and each time different files are put into my amazon bucket, but they are all in my ftp folder.
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EDIT: I just did another test, and decided to wait a little while before checking my Amazon bucket & my FTP folder. Like MAGIC! Everything worked like it was supposed to. So, I must have been too impatient before and was checking before everything was finished doing its thing. YAY!
I thought about deleting the thread, but decided to leave it in case someone else also wasn't waiting long enough before checking.