Enabling debug in 5.0.3 shows the following:
[Apr 13 17:50:05] Scanning comments with 164000 left to scan.
[Apr 13 17:50:18] Scan process ended after forking.
[Apr 13 17:50:21] Forking during hash scan to ensure continuity.
[Apr 13 17:50:21] Entered fork()
[Apr 13 17:50:21]
Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 22291813 bytes) in /home/laurenconrad/www/wp-content/plugins/wordfence/lib/wfConfig.php on line 527