In the last few versions, I cant view the custom fields box in the WP admin area.
Investigating this, I found out that the option to see it vanished only if ACF Pro is activated and comes back if I take it down or disable it temporarily.
Can you please check? Most of the time I’m using ACF, but in some cases, I prefer using WP original custom fields.
Both WP and ACF Pro is updated.
Tested on ubuntu w/ PHP7 + 7.1 & MacOS PHP 7 + 7.1.