The website is not responsive unless I put "/wordpress" after the web address

Hi,

I am using a free theme called Sydney.
My site is live and running but it is not being responsive on my phone. Unless I put “/wordpress” after the site address. I can’t figure out what could be the reason for this.. Can anyone help me?

Here is the site: https://www.seoulhosteldowntown.com/
The mobile version works only for this address: https://www.seoulhosteldowntown.com/wordpress