Dock icon shows 1 inbox item. iCal inbox is empty

My iCal dock icon on my Macbook Pro shows me that I have one iCal inbox message to respond to or acknowledge:

My iCal main display shows no inbox items:

These normally appear in the window bar where I have taken a screenshot

Quit and restart iCal makes no difference, and nor does elapsed time. So idea would be appreciated. I imagine a system restart would solve it, bit that is a bit of a sledgehammer to crack a tiny nut. Ideas received with gratitude, please

iCal is Version 8.0 (2092.3). iCal is synced to my iPhone through iCloud. the iPhone shows no inbox items