I've been in contact with Killer Tech Support. They say the problem can be resolved following a complete uninstall etc.
Here's what they wrote...any feedback appreciated.
You are currently using an outdated version of the Killer Control Center and device driver.
You should be able to resolve this by clean installing the latest version of the Killer Control Center, using our uninstaller first to remove any previous installs. This will also include the latest device drivers for any of your Killer Networking adapters. Here are the steps:
Download the latest copy of the correct installer and put it someplace handy -
https://www.killernetworking.com/killersupport/kb/faq/100-which-killer-control-center-should-i-install
Download the Killer Software Uninstaller Tool - https://www.killernetworking.com/support/KillerSoftwareUninstaller.exe. Make sure you re-download this, even if you have downloaded it in the past, as we are constantly tweaking it. Put this file somewhere handy.
Restart your computer by clicking Start > Power > Restart
Once the computer has restarted, run the Killer Software Uninstaller, and click Remove Killer Software. Once the tool is finished, it will say "REBOOT REQUIRED."
Restart your computer by clicking Start > Power > Restart
Once your machine has booted back up, access the temp directory by clicking Start and typing %temp% and press Enter.
Delete the contents of this folder. These are temporary files that are meant to be deleted from time to time - you cannot harm anything by deleting all of these files. You may not be able to delete some of these files. It is okay to "Skip All" for these files.
Using the File Manager, delete the folder that contained the Killer Control Center. By default, this folder is C:\Program Files\Killer Networking. You can delete the entire folder Killer Networking. If you cannot find this folder, it just means that the Killer Software Uninstaller already deleted it, so you can skip this step.
Double-click the installer for the latest Killer Control Center. and follow the prompts to complete install.
Restart your machine.
Test to see if the issue is resolved.
If that doesn't resolve the issue, and you are encountering an error or the installer fails when you try to install the Killer Control Center, try following this guide -
https://www.killernetworking.com/killersupport/kb/faq/90-microsoft-tool
Please let me know if this resolves your issue! If not, please reply with an updated diagnostic from your machine after updating the Killer Control Center.
You can download our standalone diagnostic application from here - https://www.killernetworking.com/support/KillerDiagnostics.exe.
Once you have the application downloaded or located, please run the application, click Start at the bottom left and then, once it is finished, click Save to save the output file, and attach the output file to your reply. Please do not copy and paste the results into your reply email. Please attach the output .TXT file to your reply, instead.