Thank you for providing me with the requested information.
The reason your post processing is not as robust or has any many features available are because mobile postprocessing is implemented as a separate code path from PC/Console post processing. This is to reflect the slower dependent texture reads, missing hardware features, extra rendertarget resolve costs, and the slower performance in general.
Which post processing effect are you faking?
Also, the feature level switch node will automatically adjust for the materials that are able to be rendered to the specific platform and shading model. I would definitely look into testing this with some of your materials to see if that resolves some of the shader compiling issue. Especially since you are developing on Mac and PC for a mobile game.
Would you mind testing with the command line as well to see if that helps?
I will do my best to reproduce the issue, but I might have more luck with some steps and a repro case where you can confirm that making a change to something like a material on the Mac, forces the PC to recompile shaders after syncing to perforce. Unless I am misunderstanding the issue, this should be pretty straightforward repro.
Thanks,