I had some errors coming in from old converter redirects in place: forumdisplay.php, showthread.php, showpost.php 

I tested some old urls and found out I was getting white pages and not found errors. I had no idea until I posted a support ticket because I saw the logs. Turns out the new converter handles redirects differently and within the script, which is good. But keeping those files in place was causing errors and probably a traffic loss. I may have missed it but wanted to share for any older vbulletin admins who converted from vbulletin with the older converter and are now running IPS 4, make sure you remove those old redirect files from the old converter and test some urls. Thank you to IPS support for a fast response and help.

It's also worth noting that when upgrading from a version older than 4.1.18 (when we moved them to being built-in) you'll be asked to remove these files if they're present.