Could you try the import after a "Delete Data" via Lightroom Preferences->Lightroom Mobile and a resign-in.
When you add new photos to your mobile device, Lr mobile needs to import the photos locally and send previews+metadata to the back-end. It seems that some of this data was not send.
If you still see the issue while processing the import could you trigger a diagnostic log.
The Lr Mobile app log can be triggered when you open up the settings and long press the to LR Icon a diagnostic log will be generated and attached to your local mail client.
Send me a LR Desktop diagnostig log - best as a private message with a downloadable dropbox link.
You can trigger the log via LR Desktop prefereneces -> Lightroom Mobile and when you hold down the alt key you will notice a generate diagnostic log button
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Guido