I have the same problem. Viewing update details for ACF version 5.8.3, the contributors list throws PHP errors:
Warning: Illegal string offset 'display_name' in /wp-admin/includes/plugin-install.php on line 737
Warning: Illegal string offset 'profile' in /wp-admin/includes/plugin-install.php on line 743
Warning: Illegal string offset 'avatar' in /wp-admin/includes/plugin-install.php on line 744
Running PHP 7.1.14.
Other plugin update screens are fine.
