Thanks, Hunter. It’s any image I try for all events, every time. I hadn’t done full conflict testing cuz it’s a pain on my live site and I was hoping this might be a known issue. So I fired up a staging version and troubleshot the sucker. Figured it out pretty quickly through plugin disablement. Confirmed on multiple browsers, in staging environment as part of playing with tons of stuff, and testing JUST this on my live site.
Two words: Jetpack Photon.
With Photon activated, all events show the lame/miniaturized image until you click over to another month, but with it deactivated they all work fine and load the square thumbnails when you first load the page.
Hopefully that’s something you can figure out a fix/workaround for, and maybe even add “fix that!” to your roadmap. : )