The Add Frames button is missing from the Frames and Arrows menu!

I have just switched to Prezi Desktop for Mac, and now working on a Prezi I find the "Add Frame" Button is missing from the Frames and Arrows Menu.

I can draw frames manually, but that is considerably more cumbersome, especially if I want consistent frame sizes.

This is extremely frustrating: this is obviously core functionality. What is going on?

I'm unsure if this is a PC/Mac distinction, or just because I have updated the software.