Mobile theme keep showing on desktop

Hello, I am using mobile theme for mobiles.
It usually is okay and shows normal desktop theme when I access my website by desktop.
However, it sometimes go to mobile theme, even if I access my website by desktop.
It usually happens after several hours from clearing the cache, or after big traffics to my website.
If I clear the cache in admnistrator mode, It comes back normally.
But, after few hours the issue happens again. I have to keep press the clear cache buttons everyday.

What can I do to solve this issue?

Thank you for your help.
I followed your instructions. I changed W3 total cache plugin to wp super cache plugin.
Also, I turned on the advanced features related to mobile theme(‘Mobile device support’, ‘Late init. Display cached files after WordPress has loaded’).
However the issue seems to persist.
The issue usually seems to happen in the posts that are most viewed currently.

Would there be any other thing that I could do to try to fix this issue?

hello, this is my website.

https://mugtimes.com

Thank you

Thank you for checking.
However the issue is still happening.
Even if it is displayed right, after a few hours or a day, the issue happens again, especially on the article pages which is popular at the moment.

Would there be any other things that I could try to fix this issue?

Thank you for your reply.
I read the articles you gave me.
I understand that It probably would be something to do with the cache.

I’m sorry, but since I’m not good at web programming or wordpress, could you please please tell me what I should change to make the issue not happen?

I have changed the cache plugin to WP super cache, which you told me that has the option for mobile devices and did the settings you told me.

But, I am not sure what to do to change in this plugin to solve this issue.

Thank you.