Hello, same issue here with DPP 4.7.2 on 2017 iMac 5k with 3.4 i5 and 8GM Ram and Radeon Pro 570 4GB video card. When I load a RAW from my new 6DII I get a prolonged spinning star from Canon program bottom right. It takes quite a while to complete even though the image appears completely and clearly initially.
I had the same issue on my previous iMac and thought it might just be out of power to process the 26MB files. My old iMac when I would make sharpening adjustment to the image it would render the image very sharp while the spinning star worked to redraw the image and then it would finish the image and it would actually de-sharpen as a final result! Yes it went from showing sharp while rendering to finishing unsharp, really strange.
The new iMac properly sharpens the files now so I have gained something that help with this machine. It's a shame, I have used the older DPP and into the DDP4 beginning with no issues. My images process fine in Photoshop with old machine as well as new. Seems that something is not correct in the initial rendering of the RAW.
I also see that unless you are running Nvidia card you can't select use Graphics Processor, seems that is something that should be updated too to allow Radeon which is in Apple iMacs.
