Upon carefully comparison between my mobiles physical file storage, and my “synced” library, I discovered at least 200 photos were never uploaded, are not syncing even after restarting the device. No choice but to manually upload them....argh.
I've had issues with modifications syncing between Lightroom CC and Lightroom Classic. Specifically, I've noticed that some modifications (flags, ratings, color corrections) made to Smart Previews in Lightroom CC Mobile don't end up syncing back to Lightroom Classic. The vast majority of my photos sync correctly, but the handful of exceptions make me nervous about relying on Lightroom CC Mobile for any serious edits.