[gallery did not import even in the middle of posts.

I used the wordpress import export tool to migrate a development site content.
I only just discovered that the [gallery] shortcode inserts on all posts and pages did not import. (bizarrely some were in the middle of post content)
The actual shortcode [gallery etc etc] code was stripped out.

I have managed to paste the [gallery] code into each post and page. The galleries are displaying on the front end but not editable in the admin. (images not found)
So the meta data has not imported properly. ( missing)
The pasted gallery shortcode is finding the images for the front end but not the admin.
Any tips on fixing this ? ..that doesn’t involve manually adding images one by one!
thanks