"Cannot Load Photo" on iPhoneX - why not?

i'm trying to open+edit a few photos (on my iphoneX) taken just 4 weeks ago, on my iphoneX.

am using icloud. have tons of remaining storage both on iphone and icloud.

i get the following error message, see attachment.

said photos open+edit fine on my imac in Photos.

this is seriously annoying... any help much appreciated, thank you! :-)