Fix Opencart 1.5.4 website error (probably Nitro cache)

Job ID: 36883252

Budget: $10 – $30 USD

The problem: during browsing the site random pages don't load on www.gyogyitokovek.eu
Homepage opens - but after you click a few products and press "Back" button on your browser, everything disappears.
Probably something is stuck in Nitro cache extension.
See uploaded error log for details.
Related categories: PHP JavaScript MySQL HTML Open Cart