I have cross checked in iPhone5,6, Galaxy S5. It’s working fine. Tell me in which mobile and in which browser it’s not showing the flex slider? So that I can have a closer look at it.
I use iPhone 5S and iPhone 5C and i have tested it on both and seems to be working fine. Please clear the cache from the iPhone and test it then let me know. or test it on another iPhone 5 and see.