Did you also modify the /etc/fstab file to point to /dev/sda2? Quite likely that's the culprit. You could also set it to boot based off of UUIDs.

It would be nice to add this in, but I don't have a spare rpi3 to blow the fuse on at the moment, so it's untested by myself.

Another thought... the resize filesystem service may not be reading it correctly as well, so if you've created the usb partitions yourself, and extended it as far as it can go already, you will want to make sure that the rpiwiggle service isn't enabled - you should be able to rm the symlink that is in (going from memory so this may be wrong path) /etc/systemd/system/multi-user.target.wants so that it doesn't attempt to resize the partition.

Pointing fstab in the right direction did the trick. Thank you for your help.

Due to the age of the OS (Kali Moto [v1], Kali Safi [v2], Kali Rolling <= 2019.2), these legacy versions are no longer supported.
We will be closing this ticket due to inactivity.

Please could you see if you are able to replicate this issue with the latest version of Kali Linux - https://www.kali.org/downloads/?

If you are still facing the same problem, feel free to re-open the ticket. If you choose to do this, could you provide more information to the issue you are facing, and also give information about your setup?
For more information, please read: https://kali.training/topic/filing-a-good-bug-report/