On your phone with one of the oder pictures, if you enter Edit Mode, can you edit the picture?
Some pictures, perhaps sent to a phone by a computer, aren't fully "owned" by Photos, and they may not synchronize with iCloud. You can often tell, because those pictures don't allow you to edit.
In any case, try saving some of these pictures to Files (In Photos, Share>Save to Files,) and then saving them from Files back to Photos (In Files, Share>Save Image.) Sounds silly, but the newly imported versions might work better, since Photos had control over their entry.
Let us know how this goes…