If I search in google with cache: www. (mywebsite).com , nothing appears in google search. however, if I use command: site: www. (mywebsite).com, it appears in google search. Why I got this weird thing? Thank you.
The Google cache feature is still works well here. I have had this issue for around 5 weeks ago but it had been resolved. Could you please post url here if you don't mind? I would like to take a look to see if I cannot see your cached page as well.
I'd look for a "nocache" or "noindex" meta element in the HTML, or HTTP headers. You can look at the response headers with this tool.