I found this in logs too
[Thu May 18 10:52:36 2017] [error] [client 66.249.66.27] PHP Warning:
array_merge(): Argument #2 is not an array in
/var/sentora/hostdata/zadmin/public_html/lib/pkp/classes/core/PKPApplication.inc.php on line 578
[Thu
May 18 10:52:36 2017] [error] [client 66.249.66.27] PHP Warning:
Invalid argument supplied for foreach() in /var/sentora/hostdata/zadmin/public_html/plugins/generic/recommendByAuthor/RecommendByAuthorPlugin.inc.php on line 114
When I turned off Recommnded by Author plugin everything worked well. I guess that plugin is making issues.
Thanks