Yes, the syncing should work both ways.
Would suggest you to follow the below steps for syncing issue:
- Go to help menu in Lightroom on your mac > choose sign out > Quit Lightroom
- Also, sign out from Lightroom Mobile.
- Relaunch both and sign in back to both Lightroom and Lightroom Mobile
Lightroom Photos that you see at the top of your collections list in Lightroom Mobile application displays all the images together from all the collections.
If you have imported your recent images in Lightroom Mobile, then yes they should sync to the Mac machine.
The time taken to sync depends on the size of the image but that should not be long.
Let us know if you face any further issues.