icloud photos - issue with uploading large groups of photos

I am trying to upload like 900 photos all together (roughly 5G) to icloud photos from my Mac, and it always failed.

But when I uploaded those photos in small groups (such as 10 photos at a time), then it worked.

Have any of you guys experienced the same problem? I could upload a small group at a time but it's just very inconvenient when you need to upload a large group of photos.

Thanks a lot