Random photos not uploading to photo share

Iphone 6s with latest ios. About half the photos on my phone are not uplaoding to my icloud / mac / ipad etc, and don't appear in photo share. Photos I took on Sunday do not appear but those taken Saturday, yesterday and today do appear.

Going back through November then there a whole days missing. I've tried connecting to Mac with usb but doesn't change anything.

This has worked for years....... Help!