The dynamic snippet works correctly only if you log in like an administrator account, snippet uses data from the odoo model. So if you log in as a public user, ooo displays a message, something like

' "Odoo session is expired. The current page is about to be refreshed." '

, and snippet uses default content from template(not data from database).

I didn't find an answer to my question in the documentation or on the forums. Please, if anyone has encountered such a problem, write how you solved it. Thank you in advance.