Since my other thread doesn't seem to be getting any responses, I'm pasting what I've found here. Please keep in mind I am not a beginner with Lightroom and consider myself very familiar with Lightroom's features excluding the new mobile sync.
I'm on Lr 5.5 and using the 30 day trial of Adobe CC to try syncing one collection of slight more than 1000 images. Despite already having generated the Smart Previews, I can see my CPU crunching through image after image (the rolling hills pattern in the task manager) while doing the sync. I was assuming, since I already created the Smart Previews, that the sync of this collection would begin immediately and be done by simply uploading all of the existing Smart Previews. The Smart Previews folder of the catalog is 871MB and has stayed the same despite the CPU obviously doing *something*. As it is now, the sync progress is incredibly slow, almost at a pace like it's actually exporting full-res JPGs from the RAW images (as a comparison only, I know this should not be what it's actually doing).
Another side effect of this is that I'm basically unable to use my computer for other tasks due to the high CPU utilization.
Win 7 x64 / Lightroom 5.5
Intel i5 2500k OC'd 4.5GHz
SSD for OS, separate SSD for working catalog and files
As a follow up, now Lightroom thinks all 1026 photos are synced (as shown in "All Sync Photographs" portion of the Catalog though all images after the 832nd image show the sync icon per image stuck at "Building Previews for Lightroom Mobile" and the status at the top left corner has been stuck at "Syncing 194 photos" for over 12 hours. Is there no option to force another sync via Lightroom Desktop and also force the iOS app to manually refresh (perhaps by pulling down on the collections view, like refreshing via the Mail app)?
One more update, I went into Preferences and deleted all mobile data, which automatically signed me out of Adobe CC and then I signed back in. Please keep in mind the Smart Previews were long generated before even starting the trial, and I also manually generated them again (it ran through quickly since it found they were already generated) many times. Now that I'm re-syncing my collection of 1026 images, I can clearly see Lightroom using the CPU to regenerate the Smart Previews which already exist. I have no idea why it's doing this except that it's making the process of uploading the Smart Previews extremely slow. I hope this time around it will at least sync all 1026 images to the cloud.
All 1026 images synced just fine and I could run through my culling workflow on the iPad/iPhone perfectly. Now I'm on a new catalog (my current workflow unfortunately uses one catalog per event) and I see the same problem: Smart Previews already generated but when syncing, Lightroom seems to re-generate them again anyway (or take up a lot of CPU simply to upload the existing Smart Previews). Can anyone else chime in on what their CPU utilization is like during the sync process when Smart Previews are already created?
Now I'm editing a catalog of images that is synced to Lightroom Mobile and notice that my workflow has gotten even slower between photos (relative to what it was before, this is not a discussion about how fast/slow LR should perform). Obviously Lightroom is syncing the edited settings to the cloud, but I can see my CPU running intensively (all 4 cores) on every image I edit and the CPU utilization graph looks different than before I started using LR mobile sync. It still feels like every change isn't simply syncing an SQLite database change but re-generating a Smart Preview to go with it (I'm not saying this is definitely what's happening, but something is intensively using the CPU that wasn't prior to using LR Mobile).
For example: I only update the tint +5 on an image. I see the CPU spike up to around 30-40%, then falls back down, then back up to 100%, then back down to another smaller spike while Lightroom says "Syncing 1 photo". I've attached a screenshot of my CPU graph when doing this edit on just one image. During this entire time, if I try to move onto edit another image, the program is noticeably slower to respond than it was prior to using LR mobile, due to the fact that there appear to be much more CPU intensive tasks running to sync the previous edit. This is proven by un-syncing the collection and immediately the lag goes away.
I'd be happy to test/try anything you have in mind, because it's my understanding that re-syncing photos that are edited that are already in the cloud should be simply updating the database file rather than require regenerating any Smart Previews or other image data. If indeed that's what it should be doing, then some other portion of LR is causing massive CPU usage. If this continues, I will probably not choose to proceed with a subscription despite the fact that i think LR mobile adds a lot of value and boosts my workflow significantly if it wasn't causing the program to lag so badly in the process.
I know this message was incredibly long and probably tedious to read through so thanks in advance to anyone who gets through it