Well one thing I see in your initial report is that the test of sync happened after changing two conditions:
- VPN off
- Rebooting the device
I’d more suspect the latter than the former (likely some Dropbox cache error that got flushed on reboot). The sort of issue we’d see with a VPN is typically more a broad denial of service, particularly if you’re using a free/economic tier, as those servers tend to be used more for spam and such, and can periodically get blacklisted by some providers.
After not syncing Scrivener projects on my iPad Pro for over six months, I reinstalled Dropbox on the iPad (having removed it to keep within the free 3 device limit when activating a new system).
By the way, you may know this already, but it’s not necessary to install Dropbox and use up one of your devices just to sync Scrivener. It uses the API directly, and doesn’t count as a device last I heard.