When multiple files with the same suffix matching another language file are included in the filePaths there is an issue matching the correct file to check.
I updated the example/multiple-files-per-locale on my fork to demonstrate this with a simple example using search-results.json and another file z-search-results.json.
When running npm run lint in that example it outputs the following errors, despite all keys matching in each file:

I tracked this down to be an issue with the code here https://github.com/godaddy/eslint-plugin-i18n-json/blob/master/src/identical-keys.js#L10-L13 and was able to solve this use case by replacing that with
const match = sourceFilePath.substr(sourceFilePath.lastIndexOf('/') + 1);