Here are a couple of commons reasons you might be having trouble shipping:
You've shipped your images to Lightroom but the number is less than what you shipped and you've never imported these images to Lightroom before
It's likely you're working with a source folder than contains subfolders. Lightroom will import your images in the same folder format so initially you will just see the images from your main folder. In the Lightroom import window, make sure you tick 'include subfolders'.
If you're shipping a large number of images, make sure you let them all load on the import window before you click the 'Import' option. This will help make your import process smoother.
If you're shipping to Lightroom but the import window isn't opening, it's possible that Select can no longer find the images in their original folder. It's possible that you've either moved the files from their original location and therefore you need to head to File > Change Source Folder to reconnect the folder that currently contains the images, or if it's a cloud source folder you will need to make sure they are downloaded (e.g. for iCloud you need to click the little cloud next to the images to download them to local storage).
If you're still having trouble with Ship, you can import your images through the following methods instead:
Highlight the selected images in Select (you can use the filters and then hit command + A to highlight them all), then drag the highlighted images from the filmstrip in Select, directly onto the Lightroom icon on your dock or the Library tab in your Lightroom app.
Import directly via Lightroom (you can use File > Copy/Move files to first move your Selection to a new folder for direct import)
If you're experiencing any other issues or the article above hasn't resolved your issue, please contact support via the chat bubble in the bottom right corner.