Hi David,

I've consult this to our developer, seems like this is bug on our end. I've logged this issue in our issue tracker and our developers will take an action for this.
Perhaps, can you try to replace the file attached in the file for temporary fix:
.../modules/mod_easyblograndompost/mod_easyblograndompost.xml
and add the categories like this: https://www.screencast.com/t/HD5KfLUD

You're suggested to backup the file that you want to replace beforehand for precaution