There is no way to sync 8k notes with Dropbox, this is your problem imho. Use Joplin Cloud instead. Dropbox sync struggles if you have many notes, but Joplin Cloud is optimized for it. When Dropbox takes 10 hours, Joplin Cloud takes 1 hour.
I have 10k notes, please check my experience here: How to survive with a large dataset on Joplin (10k notes, 20k resources, 10GB)