Longform plug-in losing scene order

This may relate to another thread that was unfortunately closed without resolution.
When I shut down Obsidian and reopen it, the Longform plug-in has kicked all the scenes out of the scene list, showing them ready to add back in. Which, of course, has lost their sequence, one of the biggest reasons for using the plug-in.
The other thread mentioned using Obsidian sync as a possible reason for this problem.
I’m using Dropbox, but have been careful to ensure that the vault in question isn’t open anywhere else, so there should be no chance of the Longform file getting overwritten with updates from another machine.
Anyone else having this problem?
Anyone managed to figure out a fix for it?