Collection cloud sync gets stuck a lot - Lightroom Classic 12.4

I use Adobe Portfolio to show my photos, and my normal process is to create a Collection in LR Classic, sync it to the cloud, then import it into a Portfolio album.

I have a lot of trouble getting my Collections to sync to the cloud. Often, the sync process would just stop, and nothing I do can make it continue. I can wait minutes or hours—the photos never make it to the cloud. On lightroom.adobe.com, the collection would show up as missing or empty while this happens. Sometimes quitting LR, relaunching it, and toggling the Collection sync off and on again would kick it off, and it would only take a few seconds to complete the sync.

Is there a reason that cloud sync gets stuck like this? Is there something I’m doing that’s preventing sync from occurring? Or is this a bug?