Undefined information when hovering over an event

STEPS TO REPRODUCE

Preconditions: Blog application is already installed.

1. Install Full Calendar Macro
2. Create several Blog Posts
3. Create a new page
4. Edit it with CKEditor
5. Click on Source
6. Paste this (year/month can be modified as required):

   {{calendar classname="Blog.BlogPostClass" startfield="publishDate" editable="false" year="2020" month="02" date="17"/}} 

7. Click 'Save & View'
8. Hover with mouse cursor over some blog posts

EXPECTED RESULTS

The hover box displays information about the Status, Location and Description for each event.

ACTUAL RESULTS

Instead of the relevant information, the Status, Location and Description display: 'undefined'.