Safari bookmarks FUBAR Mojave

"You can’t change your bookmarks right now because they are being synchronized. Wait a few minutes, and then try again."

This error message prevents me from editing Safari bookmarks. A locked thread suggests exporting the bookmarks (done), then deleting them, and restarting.

I don't want to restart, as the machine is doing 36 hours of work. When I try to delete the bookmarks, I get the exact same error message.

"You can’t change your bookmarks right now because they are being synchronized. Wait a few minutes, and then try again."

This machine is running Mojave 10.14.2