Scan can't continue – stored data not found after a fork. Got type: boolean

I just installed Wordfence on my site. I set the firewall option before I did my first scan. Then I tried a scan and it always stops with this message. I tried disabling/ enabling the config cache. I updated the max execution time to 15 secs. Still gets stuck.

Any help would be appreciated. I use Wordfence on many sites and this was my first issue.

Here is the activity log:
[Apr 18 12:31:30:1460982690.526316:1:info] Scan kill request received.
[Apr 18 12:30:40:1460982640.437457:2:error] Scan can’t continue – stored data not found after a fork. Got type: boolean
[Apr 18 12:30:35:1460982635.604029:2:info] Analyzed 2500 files containing 142.54 MB of data so far
[Apr 18 12:30:34:1460982634.532165:2:info] Analyzed 2400 files containing 139.6 MB of data so far
[Apr 18 12:30:34:1460982634.021680:2:info] Analyzed 2300 files containing 139.05 MB of data so far
[Apr 18 12:30:32:1460982632.091219:2:info] Analyzed 2200 files containing 135.27 MB of data so far
[Apr 18 12:30:31:1460982631.454465:2:info] Analyzed 2100 files containing 134.21 MB of data so far
[Apr 18 12:30:30:1460982630.239845:2:info] Analyzed 2000 files containing 132.91 MB of data so far
[Apr 18 12:30:29:1460982629.689864:2:info] Analyzed 1900 files containing 130.98 MB of data so far
[Apr 18 12:30:29:1460982629.440742:2:info] Analyzed 1800 files containing 129.85 MB of data so far
[Apr 18 12:30:29:1460982629.231850:2:info] Analyzed 1700 files containing 129.36 MB of data so far
[Apr 18 12:30:29:1460982629.040092:2:info] Analyzed 1600 files containing 129.08 MB of data so far
[Apr 18 12:30:28:1460982628.891390:2:info] Analyzed 1500 files containing 128.56 MB of data so far
[Apr 18 12:30:28:1460982628.737541:2:info] Analyzed 1400 files containing 128.49 MB of data so far
[Apr 18 12:30:28:1460982628.467646:2:info] Analyzed 1300 files containing 128.19 MB of data so far
[Apr 18 12:30:28:1460982628.303777:2:info] Analyzed 1200 files containing 127.67 MB of data so far
[Apr 18 12:30:28:1460982628.119252:2:info] Analyzed 1100 files containing 127.12 MB of data so far
[Apr 18 12:30:27:1460982627.922972:2:info] Analyzed 1000 files containing 127.01 MB of data so far
[Apr 18 12:30:27:1460982627.785680:2:info] Analyzed 900 files containing 126.78 MB of data so far
[Apr 18 12:30:27:1460982627.533417:2:info] Analyzed 800 files containing 125.37 MB of data so far
[Apr 18 12:30:27:1460982627.235917:2:info] Analyzed 700 files containing 123.32 MB of data so far
[Apr 18 12:30:26:1460982626.656965:2:info] Analyzed 600 files containing 109.99 MB of data so far
[Apr 18 12:30:23:1460982623.788427:2:info] Analyzed 500 files containing 6 MB of data so far
[Apr 18 12:30:23:1460982623.609119:2:info] Analyzed 400 files containing 5.44 MB of data so far
[Apr 18 12:30:23:1460982623.404741:2:info] Analyzed 300 files containing 3.91 MB of data so far
[Apr 18 12:30:23:1460982623.141806:2:info] Analyzed 200 files containing 2.34 MB of data so far
[Apr 18 12:30:22:1460982622.959501:2:info] Analyzed 100 files containing 1.21 MB of data so far
[Apr 18 12:30:21:1460982621.562146:2:info] Found 8 themes
[Apr 18 12:30:21:1460982621.554654:2:info] Getting theme list from WordPress
[Apr 18 12:30:21:1460982621.552434:2:info] Found 15 plugins
[Apr 18 12:30:21:1460982621.527881:2:info] Getting plugin list from WordPress
[Apr 18 12:30:21:1460982621.225597:1:info] Contacting Wordfence to initiate scan
[Apr 18 12:29:54:1460982594.343888:1:info] Scan kill request received.

https://wordpress.org/plugins/wordfence/