The problem seems to be caused by your server performance. Because of slow loading, most resources can’t be loaded correctly. Sometimes it works well and sometimes not https://gyazo.com/aa01d2d7d72d301f871af398ba5cbd8f
We suggest you to contact your hosting provider and ask to investigate the problem. Average admin page loading time is 50-60 seconds while it should be loaded in 3-4 seconds.