Ok, I think I stumbled across a bug.
1. Checked the mysql modx2_site_tmplvar_contentvalues table and noticed that unchecked TVs didn’t have entries in the db.
2. Turned on a default value of "0" for the TV
3. Went into each of the resources in question, checked the box, saved, unchecked the box, saved. This created db entries. I would have expected these entries to have a value of "0" (the default value), but instead they had a value of null.
4. Modified code to look like this:
[[!getResources? &parents=`[[*id]]` &depth=`0` &tpl=`eventListing` &limit=`100` &includeContent=`1` &includeTVs=`1` &tvFilters=`eventIsFeatured==` &sortbyTV=`eventStart` &sortdirTV=`ASC` &sortby=`` ]]
This would then pick up the empty checkboxes in the getResources call.
5. Created a new resource and left checkbox unchecked. This did not create an entry in the DB with the default value.
6. Looks like it’s time to do something else