Yeah, the underlying query syntax in Couchbase Lite Core uses a few ‘magic’ property names like
_sequence, etc. to represent metadata. When you query a real property with such a name, it gets confused with one of those.
I could add a way to escape the underscore. But even if I do, you’re going to run into problems when you try syncing with a server, because Sync Gateway has a very hard restriction against any top-level property starting with “_” … and this restriction is tied up with its REST API and couldn’t be relaxed without making significant changes to that API, i.e. not gonna happen.