Issue: Connection error on edit of specific wiki article

While I can reproduce on your site, the same issue does not occur for me when copying the BB-Code source to a test board, and there are no error messages in XenForo logs, suggesting a higher level error separate from the application itself. Please trigger the error and check your internal Apache and PHP error logs for segmentation faults (Apache or PHP crashing). If a crash is occurring, you will have to report the issue to Apache or PHP devs.

Make sure you have not enabled php.ini's opcache.fast_shutdown. It is known to cause issues like this.

A similar issue is known to happen in Chrome when the server's SSL configuration uses certain cipher suites: https://forums.cpanel.net/threads/ht.../#post-2454643

It is also possible to get a server to reject requests if the request exceeds some limits you have set in your configuration, such as firewall, Apache, or PHP limits on the size of POST variables.

I can duplicate the issue in a standard forum post on your site by copying the same BB-Code into it. Removing the superfluous COLOR and FONT tags seems to resolve the issue. This may be a hint regarding what firewall/server rule you may be hitting. Improperly or deeply nested HTML tags in user input, specifically FONT and SPAN tags, may be triggering the rule, or it may be related to length, and removing the inappropriate tags coincidentally lowers the length enough.