Hi Koyuki Matsunaga,
Have you configured a page ‘onclick’ of a row on the grid? If yes, the configured page data load taking more time on the onclick page. Generally if you have configured a widget on a page that has to load more data, results to freeze the screen for few seconds.
Hope this helps to figure out your issue, Thanks!
It's quite difficult to tell since we don't know what other kind of elements are on the page. What you can do is open your Console in Chrome (with F12) and check your console or network tab if things are still loading. If that is the case you can check what element it is and investigate further why it's loading so slow.
Hope this helps.