I have a very large mosaic dataset that I am uploading to AGOL. I have been successful in uploading it before and have no issue in that regard. It does take time, an hour or more but that is OK.
My issue and question is if it is possible to configure the uploading parameters so that is doesn't hog all the network bandwidth? As it uploads it will consume 96-100% of the available network. As you can imagine, this slows down everything else preventing me from doing other work while I wait for the upload to complete.