Hello there,
Good Day!!!
We unable to reproduce your reported issue from our side, could you please troubleshoot the following steps
1. Check your SPAM Folder.
2. Deactivate all other plugins except WooCommerce and our Back In Stock Notifier.
We also keep record each activities of our plugin as log – Please check that as well whether automatic email part really triggered in your side as per the status change(out of stock to instock)
Log can be checked here Admin Dashboard -> WooCommerce -> Status -> Logs – In there top right dropdown find the prefix back-in-stock-notifier with latest date has all the information about the process(post that as well for further assistance).
Thanks.??