Bad requests getting my users blocked

Some of my company’s clients are being blocked by WPEngine when they attempt to navigate to our tutorial content. I’m not sure if it is related to the browser (more on that) or if it is related to multiple tutorials being embedded on this page.

When I access the Apache and PHP error logs, I’m seeing upwards of 400 errors within millseconds. Here is an example error (out of 436; I’ve concealed the actual IP):

[Tue Jul 24 14:29:33.248890 2018] [autoindex:error] [pid 23974] [client XXX.XXX.XXX.X:19703] AH01276: Cannot serve directory /nas/wp/www/sites/alliedtelecom/wp-content/uploads/articulate_uploads/Allied_Communicator_Android_Tutorial/: No matching DirectoryIndex (index.html,index.cgi,index.pl,index.php,index.xhtml,index.htm) found, and server-generated directory index forbidden by Options directive, referer: https://www.alliedtelecom.net/wp-content/uploads/articulate_uploads/Allied_Communicator_Android_Tutorial/story_html5.html

When I check the Apache log, I see items like this:

XXX.XXX.XXX.X - - [24/Jul/2018:14:29:33 +0000] "GET /wp-content/uploads/articulate_uploads/Allied_Communicator_Android_Tutorial/ HTTP/1.0" 403 284 "https://www.alliedtelecom.net/wp-content/uploads/articulate_uploads/Allied_Communicator_Android_Tutorial/story_html5.html" "Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; rv:11.0) like Gecko"

Take note that the common element I’m seeing in these cases is the user agent being used to request the tutorials, which is IE11 on Windows 10. My theory is that IE11 is choking on the HTML5 content, most likely due to the script that handles the Flash/HTML5 fallback procedure.

So far I’ve had about 4 clients and our own company’s IP address blocked. Anyone who hosts with WPEngine is also likely to experience this issue, whether they know it or not.

The page I need help with: [log in to see the link]