When updating to v9x (9.10+) the MacOS screen capture permissions may need resetting in order to function correctly if you have used a AB Client previously on MacOS.
A quick and easy way to do this is to select the affected Client in your Console and make use of the Command prompt action to reset permissions with the following commands:
tccutil reset ScreenCapture com.abtutor.client
tccutil reset ScreenCapture com.abtutor.console
Doing this will reset permissions and require the user to manually accept the screen capture prompt. Rebooting the Client should make this happen reliably. You can use the "Shutdown" action for this also.