me too! This issue is blocking my use of google photos 2TB. I just made hundreds of family holiday photos and videos, to store for future fun, only discovered after getting home several were partially uploaded. Sadly, I already removed the original photos from my iPhone photos app, to free up storage for more shots. So I have no way to restore the high res pics/vids.
Google photos will not let me "re-upload" or re-initiate/resume the partial upload ... real bummer.