Urgent need help! Why the RWD doesn't work right on Navigation bar?

I designed a site for my portfolio, and everything work well. However, when I test on iPad, my main page looks good, but the other pages navigation bar doesn’t become hamburger form, and only happened to iPad. Wonder to know do I miss some setting? How to fix?

And here is my read-only link

Many thanks

Hey @HSUANHSUAN_HO , it looks good on my end. Could you try to see if you can replicate the issue in incognito mode or a different browser? Could possibly be a weird cache issue because it works fine on my end.

Many thanks for your reply. I will try.
Could you kindly post the screenshot here for me, please?

For sure @HSUANHSUAN_HO , see me screenshot below.

many thanks for your help.