I am afraid, you are stuck as all of us. I have 123 files with sync problems since the early beginning of Adobe Cloud. And Adobe is doing nothing visible to clear this long lasting issue. I just hope that ON1 360 will force Adobe to reconsider their “do nothing’ position” and then work on making Cloud operation simple, straight forward and unable. If you prefer, I speak French and can explain what happens in French.
I feel your pain. I tried each and everything suggested here by other users and Adobe support alike, and NOTGHING worked. Not one thing! Finally, I gave up and decided to risk losing all my sync states and simply try something different. Here's what worked for me:
• In Lightroom CC Desktop:
– Pause Syncing (also on any mobile devices)
– Mark all your synced collections with a temporary color to remind you what you had synced before. I used yellow. It is quite a chore, as I have many Collection Sets and nested Collections.
– UNsync each of these collections.
• Sign out of all Adobe CC apps (desktop and mobile and Web)