photos won't upload

I bought a 2tb icloud plan specifically because i wanted to backup and keep my photos in the cloud. My mac spent five days uploading, then came up with a message that 22034 images could not be uploaded, and those pictures are in a «can't upload» folder. That's roughly half my images. (Have been using iphoto and then photos since 2001)

Obviously I have too many images, and need to do some deleting, but that's a long term project:)

The photos in the folder are all kinds, raw, videos, portraits, iphone and camera pics, so there seems to be no system as to which fail to upload.

I have googled, but none of the «tips» seem to apply to my situation. I use a macbook pro and have my photos library on a portable HD which is set as the system library (the library doesn't fit on my Mac HD, it is too big). Obviously something is working, since half the photos did upload. But what do I do about the rest? There is no «retry» button.

How do I solve the problem? If I can't upload these pictures, icloud and photos seem pretty useless to me.