In Software Only - Color Correction Mode: Fullscreenplayback only shows the current picture, but not the left or right monitor for Previous / Next / Reference. It's bee like that a while, now also in 2023.3.0. 

It's working with IO hardware but not in Software Only mode.

Hmm interesting. This is one I'll look into. 

Does this happen on your machine or multiple machines? 

With the later versions you can actually full screen playback in software while running MC in hardware mode (having an I/O card connected) so wondering if it would work on a system running software full screen playback with an I/O box attached aswell. 

I'm now on a different machine, also MC 2023.3 / OSX 12.6.3.

It's buggy, but it seems to work best when you have an I/O attached and deactivate / activate that. 

But in my case I'm either working with IO in my studio, which is fine or working in Software mode at home, which is buggy.