I may have found a workaround, at least for my use case, which is backing up stuff from the SD card to other machine(s).
- Set up the sync folder as "Folder Master" / "Send Only".
- Manually create or copy an existing
.stfolder into the folder.
- Cross fingers.
It hasn't finished syncing yet, but it has finished a scan, and has started transferring data. I'm going to let it run overnight and follow up in the morning.