Apologies for the delayed response. For some reason, I missed this topic when initially posted. I aim to respond to all questions within one business day so if this happens again please feel free to post another message in the forum to get my attention. Again, sorry about that…
It looks like you are using another theme at this moment. When the issue with the non-appearing menu occurred, you using the Adaline theme as demonstrated at this URL? https://adalinedemo.wordpress.com/
As for why a menu wouldn’t display, that could be because either a menu was not assigned to the sole menu location in the Adaline theme, or there were no pages published on the site.
If either of those were the case then this could be an issue with other WordPress themes as well.