Some phone Gallery photos cannot be seen from within Lightroom mobile

I recently installed Lightroom Mobile for Android V 6.2.0 on my Samsung Galaxy S8 phone.  I also have LightroomCC installed on my desktop computer (also recently installed). My plan is to use LightroomCC cloud storage as my repository for phone photos. Initially, I copied all the photos on my phone to my desktop, where I also had folders of photos from previous phones. I imported all into LightroomCC.  I could then view all the photos from either LightroomCC on the desktop or Lightroom Mobile on the phone, and everything appeared to be syncing fine when adding or deleting photos from either program. 

Since then I have added photos from within LRMobile using the add photo icon, then selecting phone gallery photos and adding them. Today when I attempted to do this, LRMobile does not detect all the photos in the Gallery--I have 18 new photographs taken on March 22 but LR mobile sees only 6 of these 18 photographs.  

How can I fix this?