Original Photo File Has Gone - HELP

I am using Photos 2.0 on my Mac and have noticed that a number of old photos have not synced across to my iPhone X.

 

For example : I have a holiday to Australia with 270 photos in Photos on my mac but only 45 of them have synced to my iPhone X

 

I went into Photos 2.0 on my mac and reviewed the album and found that the photos that haven't synced are the ones I am unable to edit. I then tried to drag one of the photos onto my desktop but I got the following message:-

(see photo)

 

Export complete with errors

The export operation failed to create a file for the photo identified

'The file "P100000030.JPG couldnt be opened because there is no such file"

 

I assume over the years having messed around with the library in the past I have lost the original file of the photo and what i see in Photos on my mac are Thumbnails ?? (despite the photos looking normal size and good quality)

 

What I would like to know is am I able to do anything with these photo thumbnails now as I don't have the original file for some reason?

 

I have tried copying the photo from Photos to try and create a new file version of the photo but again I get the message that there is no original file which is really frustrating.

 

Any help of a way around this would be appreciated

 

 

iPhone X, macOS High Sierra (10.13.2)