I found this PHP error:
[Fri Jan 18 14:59:13.104063 2019] [php7:error] [pid 15167] [client 10.161.51.171 :53535] PHP Fatal error: Cannot use ‘String’ as class name as it is reserved in /var/www/html/mcyzykOjs/lib/pkp/classes/core/String.inc.php on line 57
OJS 2.x and PHP7 don’t mix?