@Midphase - AMD openGl drivers are full of bugs and it's best to have specific combinations of hardware and drivers tested. i.e. with a AMD7950 OGL viewport selections where unusable a mere 3-4 years ago.
to be clear MacOS OpenGL is the issue here. AMD OpenCL is perfectly fine afaik. e.g. the Vega in the iMacPro already has a bug that delays viewport de/spliting so that rules out Vega cards for the moment.