After looking at the OpenASAR Github Page, I found this post on an issue report which helped me out:
Following this, I then ran Discord as normal, without OpenASAR first, and then the OpenASAR version started working again. To do this, I ran these two commands:
$ export NIXPKGS_ALLOW_UNFREE=1
$ nix run --impure nixpkgs\#discord-canary
It seems like there were some things that Discord Canary does for the first time after being updated to a new version that OpenASAR wasn’t doing. I can now declare this issue solved, and I can now run Discord Canary with OpenASAR as normal.