I sync'd a collection just fine. Then I created another collection with some of the images from the sync'd collection but the subset collection is not syncing. I logged out and back onto adobe and also restarted computer. Do you know what the problem might be?
Possibly you cannot 'sync' the same photo twice- Lightroom sees it as a duplicate. (Both Collections are referencing the same photo file!)
How do you know it isn't syncing? What steps did you make to sync the collection? Have you check for it at Lightroom on the web at lightroom.adobe.com? I frequently sync collections with images that are also synced in other collections without any problems.
I knew it wasn’t syncing because the new sync’d collection was not showing
up on the Lightroom mobile app on multiple devices.
David M. Rosen
Disregard my earlier reply re "duplicates"!
It occured to me that different Classic Collections may list different Virtual Copies of the same photo.
And I realize I do have different versions of the same photo available in Lr-mobile apps.
So follow advice from Theresa_J
go To the Lightroom preferences > Lightroom sync. If there are images stuck in the sync process they will be listed in the section below. Whatever is listed is a link to the image in the catalog, so you can click on it to find out what exactly is stuck.
You can rebuild the sync data by clicking in this area with your alt or option key.
You should also visit Lightroom.adobe.com. What you see here is what has synced. If you see the collection in question here and not on your mobile device, then the problem is with the device, not with Classic.