The network system in bootstrap v4 does not work on iPhone 5s (iOS 9)

Question

The mesh system does not work with both Google Chrome and Safari on the iPhone 5 with iOS 9 installed.

We use the Bootstrap v4 alpha-6 SASS version with only the files we need included. The website works on all other devices: desktop, laptop, tablet (iPad and Android) and other mobile phones (Android, Windows Phone, iPhone 6 with iOS 10).

• Operating System: iPhone 5s (iOS 9)
• Browser: both Safari and Chrome
• Website: https://www.poljinos.hr/en/

The problem is the grid, it displays all col * elements on one line, and the website is over 100%.

Any suggestions why this is happening?