I’ve found the trigger which is if the initial thumbnail fills the width of the page, an error will occur during calculation for thumbnail grid sizing. I’ll look at a proper fix for this problem but in the meantime, you can work around it by reducing the thumbnail scale setting.
- Open Exhibeo document
- Show the theme settings
- Expand Document Settings
- Reduce Thumbnail Scale to 180%
This should make max-width small enough that it won’t trigger the problem on the vast majority of devices.