Further info..... I also get hang when I preview a clip selected from the project assets pane and then attempt to close the preview pane. I can avoid this if I leave the pane open and select the next clip I want to preview. It plays Ok. So the workaround is never to close the preview pane, Similar to Pan Zoom on stills. If I just press Done Its Ok. If I preview and then done it hangs. I am pretty convinced its recent iOs update as videos projects that did work now hang. Is anybody else getting this. Its strange to believe its only me!!.
I will answer my own question to close it down. After lots of research I am forced to the conclusion that the only fix is to upgrade to Premiere Elements 2018. I am informed this works with High Sierra and is obviously still supported by Adobe