When opening a document in Illustrator on my iMac is only showing a gray screen. The tab bar has the file name but will not show the artwork in that tab. I can select all the art and copy from that tab and paste in a different tab and the artwork will show up there. Usually the only fix to get this to work is to quit Illustrator and restart it. This only works for a few documents and then it starts all over again. I just updated to the newest version yesterday 8/21/2019.