hi there - sorry for the troubles :(

we initially had plans for a warning about that, but first feedback said that people like to have a second tab open for a 'readonly' version during writing, and that locking it off would disrupt that workflow (and also, figuring a way to lock a project from being open multiple times is a bit harder when adding multi-browser/-device to the mix).

at the moment, NC is not a real-time application - like in google docs, where many people can work on the same document at the same time.

as such, currently, never ever use two windows for the same project at the same time. this can lead to data loss - but: can you check the revision history on the scene to see if the content is still all there?

There's a good chance that your writing is still all in there, and just got overwritten from the other tab.