theme preview sometimes shows default theme (twentyseventeen)

[progmastery]

When clicking preview button in theme page
​https://wordpress.org/themes/business-elite/
Instead of theme preview, twentyseventeen preview is displayed.

​https://gyazo.com/793ca191cd9cbdae61d0aae9d2c4f3a1
This happens with different themes, but not always, occasionally.
Just click to see theme preview and you will see sometimes default theme.

[SergeyBiryukov]

Related: #145, #395, ​#WP20514.

[progmastery]

Replying to progmastery:
This happens on homepage of the theme preview. Just go to theme page and click preview. If everything is ok, go back to the theme page and repeat the previous step until you occasionally see default theme preview.
Browser chrome 57 windows, cookies enabled. There is no tab with other theme.

[dd32]

This should've been fixed recently, one of the servers had an out-of-date theme cache. So you'd randomly get the default theme when it couldn't find the requested theme.