I can't get sync to work with many folders & notes

That doesn't surprise me. However, I've got a reasonable sized database of 3732 notes, 5554 note tags, 192 folders, 3422 resources. I've had no issues syncing with dropbox for over year and at least 2 years with Joplin Cloud. I sync 2 android tablets, 1 android phone and my desktop computer.

If I don't keep them in sync for a week or so, then it can take a few minutes to sync with my older tablet. My newer tablet which syncs every day, doesn't take longer than a few seconds using Joplin cloud.