Essentially everytime you launch a WoW game client, another invisible window with the same name is launched and you end up renaming and sending keystrokes to those windows instead of your game clients.. This is just something WoW does for whatever reason. It began somewhere mid Legion I believe.

There were plenty of threads about it during the time and people suggested different solutions to the issue. For example here: https://www.dual-boxing.com/threads/...oW-Stress-Test in post #3 someone suggests just adding more renaming lines to your script and that is apparently working for them.

HKN is fading out in popularity, so not many people who actively use these boards actually use it anymore. Due to it having been out of development for years and ISBoxer offering what is generally considered a better experience it's more or less a niche software at this point...