This is just a tip for iOS 12, not a complaint. I’m sure you are getting around to fixing iOS 12 stuff as it comes, so I hope this helps!
Using iOS 12 with Agenda app, latest update: Checkboxes are pretty hard to tap on iOS 12 (like less area to tap on to tick the box) and when I do finally tap it (by holding for a quick second) it distorts the little circle into an oval (with a light grey circle behind it) and then ultimately appears “checked”.
This was not occuring before I installed iOS 12 beta, it was very easy to tick the boxes and no “stretched circle” during animation.
Hope this helps!