Hello @haywardgb thank you for letting us know this affected your ability to complete the challenge also.
We found that while this challenge was live, our QA team were unable to replicate the issue and the challenge was completed for them.
The next time you encounter any issues with certain challenges, registering certain types of kills, please let us know and record another video if you can, and we will report this asap.
I am sorry we were unable to resolve this while the challenge was still live.