Still looking for help here!
Generally speaking, syncing (uploading) should work fine, though of course the speed is totally dependent upon your WAN upload speed. However, for a few weeks I kept running into a problem of the upload "stalling" after a few (10-20) raw files had been uploaded. Close and restart and it would do a few more before stalling again. It quickly became apparent that something was happening with my network router, i.e. it would disconnect from the WAN, then restart the connection. Obviously there was a problem of some description with the LRCC's use of the router, because the disconnect/restart only happened when uploading from LRCC. I swapped out the router and the problem went away. But when having these "events" LRCC did not recover when the WAN connection was restarted (possible bug?), hence the need to restart LRCC to get it to sync again.
This may be totally unrelated to your problem, but thought it worth mentioning. When your syncing stalls, does it resume if you simply restart LRCC?
I don't have any advice/help with your sync problems but your post prompted a question I've been asking of myself (no good answer yet) and you seem a good candidate to maybe help?
I assume you have 1000s of images stored on your computer drive(s) - so do I.
Most of those images (some long ago) have been processed for print, email, online viewing, selling, etc.
So my question: What do I gain by having all those images stored 'In the Cloud'? I'll never view most of them on a mobile, I'll never process most of them on a 2nd computer.
Would I not be better off just sending those images to the cloud that I intend to process/view/share on a 2nd computer and/or view via mobile and just leave the rest to rest on my Pc's drives?