Courses and course formats

Not sure if others have experienced this, but I have a site running v3.8+, and has topics format, single format and Tiles format.

In any course (any format), if I turn on editing and add an activity or resource I can see it on the page. If I turn off editing it is visible in Tiles format, but not topics format. The topic has some text on the right hand side telling me an activity is there, but the topic itself is completely blank... just the title. Nothing hidden, no restrictions in place, just a plain old Moodle system, using the 'Maker' theme from 3rdwavemedia.

I use that theme in other sites - same versions, etc - and it works.

So I was wondering if anyone had any useful insights into this sort of thing... I've not experienced it before... what might I be overlooking?