I think I have found the bug that you described in my “WaniKani Item Info Injector” library script that “WaniKani Pitch Info” uses. I have fixed it and will create a pull request for “WaniKani Pitch Info” to update to the newest version of “WaniKani Item Info Injector”.
You can either wait until the script author accepts my pull request, or you can install “WaniKani Item Info Injector” directly to immediately use the newest version.
Also, if it still does not work after the update, let me know and I will look into it.
EDIT: I had forgotten that the script author of this userscript has already given me write access to the repository. Version 0.56 of “WaniKani Pitch Info” is up and contains the fix.