Slitherine

I just downloaded the MAC version of the game from the Slitherine site (not the Steam version)
When the game loads up, I get all the intro screens and the main menu...but when I try to play any scenario or the Boot Camp, it takes me to a "blank" map screen.
(I see a map of the Pacific Ocean) but there is no writing, buttons or "thinking" going on. I just hear music and see my cursor arrow and nothing else. Am I missing something?

Do I have to play via Steam? Or is their a fix for this?
I wanted to give the game a try before purchasing other Campaigns. (I love playing PzC on my old PC) but was looking forward to this game on my iMac.

3.6 Ghz - Intel Core i5
16GB RAM
Yosemite 10.10.5
ATI Radeon HD 5670 512 MB

I've searched the Forum...but not sure I can pinpoint this problem.
Thanks for any help.

I play on a late 2009 iMac without any issues... Perhaps it's related to Yosemite, which is a couple of generations old - I run on Sierra.

I opted to download the STEAM version....it works fine now. Enjoying the game.