Good news for you, I use Hestia too and that happened to me too. No, it is not that your site is hacked. It was because of the upgrades. Your website got upgraded to the latest stable PHP version and staff had to rush it because apparently there was a security problem.
Your navbar hasn’t disappeared, it has just been dislocated. Fix this by adding a location for your menu bar.
Happened to me top. Using a child theme would fix a problem like this in the future (helps with upgrading themes too without customizations disappearing) Just check the child theme guide: