I too am having trouble with Lightroom Mobile after a few problem-free months. I'm running LR 5.6 on Windows, plenty of memory, etc.
I have marked collections on my desktop app for sync and I am signed in/sync on. but no sync. There are no files in the cloud and no sync activity showing on the desktop program.
I've tried signing out and in, creating new collections, deleting all data through Edit/Preferences, deleted and reloaded the IPad App. Can't think of anything else.
Has anyone any suggestions?
Thanks