Are you signed into LrMobile on the desktop? Is the collection sorted in Comment Order? Can you see their favourites in LrWeb or in LrMobile?
I can see their favorites in LrMobile but not on my desktop. I am synced with LrMobile.I do not know in what order the collection is sorted. Just the regular i think, i haven't changed anything.
Are you signed into LrMobile on the desktop? Another way of saying it - are you in the right catalogue, the one that syncs with LrMobile? If you are in the right catalogue, is Sync paused?
In the Toolbar, change the sort order to Comment Time. That should let you identify the favourites more easily.