Global Author Posts Feed urls are returning 403 errors

Good afternoon,

The feed urls generated by the WPMU Global Author Posts Feed plug-in are returning 403 errors. I have it installed on 3 multisite installs (blogs.duanemorris.com, ercoats.wpengine.com and dmsandbox.wpengine.com) and all 3 are returning 403 errors.
All 3 installs were upgraded to WP 4.7 last week. I'm not sure this breaking coincided with the upgrade. According to your website, the plug-in is compatible with 4.7.

Seems that something regarding permissions has changed. My sites are hosted by WPEngine. Their support was not able to resolve this issue via live chat, so they opened a ticket and also advised me to open a ticket with you as well.

Here are example urls from all 3 installs:
http://blogs.duanemorris.com/feed/globalauthorpostsfeed?author=54
http://dmsandbox.wpengine.com/feed/globalauthorpostsfeed?author=3
http://ercoats.wpengine.com/feed/globalauthorpostsfeed?author=3

I've uninstalled and reinstalled the plugin on ercoats... didn't fix it.

Also, every time I try to access one of these feed urls, it writes an error to error log, e.g.:
[Wed Jan 04 17:06:30.232856 2017] [:error] [pid 18501] [client 12.144.20.254:36320] preventing possible attempt to enumerate users
[Wed Jan 04 17:06:57.952458 2017] [:error] [pid 31845] [client 12.144.20.254:36904] preventing possible attempt to enumerate users, referer: http://blogs.duanemorris.com/wp-admin/network/users.php?s=sinrod

Any help in resolving this issue is greatly appreciated.

thanks,
Denise Tucker