Sorry for the late reply!
The mobile menu is working correctly on my testing website. But the icons are missing and they are replaced by random text like in the screenshot below;
The reason behind this, the font icon set is not loading. As a quick fix, open functions.php
and scroll down to line 120 then change this line;
wp_enqueue_style( 'materialicons', '//fonts.googleapis.com/icon?family=Material+Icons', false, null, 'all' );
wp_enqueue_style( 'materialicons', 'https://fonts.googleapis.com/icon?family=Material+Icons', false, null, 'all' );
In the past the previous code used to work but now it doesn't load all required font files, it only loads the font CSS file. Maybe Google has removed redirects from HTTP to HTTPS for their static resources or something similar because this code was working since the release of Realistic.
Of course you need to do the same to load Roboto font;
wp_enqueue_style( 'roboto_google_font', 'https://fonts.googleapis.com/css?family=Roboto:400italic,300,700,400', false, null, 'all' );
For the off canvas menu it's working on my website;
Edit: By the way, I have an update for Realistic that I am currently testing but please not that a lot of files were changed and functions removed/renamed so if you are extending Realistic using a child theme, make sure you test the update because you will receive and error or blank page if in your child theme calls a function that is no longer available/defined. This update should come out very soon. Maybe tomorrow at most.