It seems that the images are missing from the catalog in Lightroom.
Please follow the below steps.
> Open Lightroom and go to Library mode
> In the Folders panel in the left hand side, you would be able to see the folders with question marks "?"
> Make a right click on the folder and Choose Find missing folder (it is best to locate the parent folder)
> Navigate it to the current location of the folder
It will remove the question mark and the folder will be added to the drive accordingly.
Let me know if this helps.
Thank you Mrinmay - Is the process the same for missing photos in folders as it is for missing photos in Collections? I cannot find anything in the literature on missing photos in Collections -- everything refers to missing photos in folders.
Once you will have all your folders or images connected to Lightroom, you will not have to make any changes in Collections.
It will remove the exclamation mark(File Missing symbol) automatically in your collection.
Hope this helps.