Header display in Ample 1.1.0 at the time of use iphone6

wordpress version 4.4.2
Use theme Ample 1.1.0 Free (child theme used)

Thank you for your help.
We are running a site in the above-mentioned contents, but happening events, such as the following.

At the site of the blog TOP page, and in the header section title
Navigation menu does not appear.
However, only becoming the case of the following at the moment is not displayed,
Cause is in trouble not grasp.

Use site is here
https://www.old-sac.com/staffblog/

No browser display problems with the PC
Smartphone display on the PC (firefox UA switcher) no problem
Smartphone display on the PC (chrome developer tools) no problem
Display of a smartphone actual (android) no problem
Display of a smartphone actual (iphone5) no problem
Display of a smartphone actual (iphone6) NG

Does not change the situation even try to switch the child theme to the parent theme.
Also, did not change even if the clear all the css of child theme.

Be allowed to view the distribution source of the demo site, it seems to be the same event.
https://demo.themegrill.com/ample/

If you also be the case distributor, it will then also feel like not a theme factor
Is up to that was an inquiry towards here.

I hope you can be good ideas from everyone.
Thank you very much.