Q: photos on MBP will only upload a few of my selected photos to iCloud sharing folder, why?

I created a folder in photos on my MBP to add some pictures to, and successfully added the photos there.

I created a shared iCloud folder. I tried adding these same pictures to the shared folder, however, zero to about 15 (of 369) photos get added to the shared folder.

I've tried several ways to add the photos, selecting, drag and drop, select and created shared iCloud folder, always same results.

How can I fix this?