Part of page falls off after update of catalogue items, but not every time

Hi,
I am not very skilled with web development, so I imported demo data of Enfold one page restaurant theme, and recreated the site with my photos, my menu, contact details, forms.

The problem: when I am updating #menu part, when I press update,
SOMETIMES part of the page falls off, sometimes not.
When it falls off, I go back to ok revision with full page, and update page back to normal, then add 2 more lines of menu, then update, then it is ok, then add 2 more lines, and it is ok, …..it happens without any rules.
I was wandering if it has something to do with autosave functions of WordPress, and searched on the internet, solutions for this problem, added this line to config.php: define( ‘AUTOSAVE_INTERVAL’, 300 );
BUT it did not help, same is happening again and again.
I noticed that even when I get back the whole page, first part of the menu does NOT have bold catalogue items, and items ARE bold, EXACTLY at the place, where page is falling off.
I looked into settings of color section, and in catalogue item settings, and they are the same as in parts of the page, which is not falling off.

Thx in advance.
Best regards,
Alex