for the video files how long did you wait? the max transfer speed for the stick is only 6Mb/s so large videos will take a while to transfer.
when you are trying to transfer many files at once does it seem to hang on any particular file? if you try to transfer that file by itself will it transfer normally?
were all the files taken on the iPhone or are they from other sources? are there any edits or filters on any of the files? Live photos?
have you tried the stick on any other iOS device? do you see similar issues there?
also I would suggest uninstalling the connect drive app and reinstall. once that is done power cycle the phone and try the transfers again.
