Well, I've done it again: Foolishly immediately updated to the latest version of Premiere Pro CC 2018 while in the middle of an important project (video of granddaughter "helping" to build a doghouse). I had a good reason though (see my post on rendering to prevent a crash).
Premiere Pro CC 2018 immediately showed a problem. I loaded my video-in-progress and PP2018 noted that it had to be converted. I said OK and all seemed to be well. Remembering problems with crashes, I immediately saved the converted video project. Now, my practice in such cases is typically to do a "Save As" just to be sure of where the files will be saved. Of course, there was a duplicate file name and I said to replace it. PP2018 immediately crashed, errors generated, file sent to Adobe, etc. Rebooted and tried to open the Save As file but all my clips had been combined into one. Tried again but, of course, same problem. Made a new project, loaded one movie clip, saved (OK), did a Save As, screen went blank but no crash. PP2018 screen stayed blank.
By now, I've uninstalled PP2018, reinstalled and repeated the various "tests" all to the same problem. As far as I'm concerned, you can't do a Save As in PP2018 but a simple Save is OK.
Wish I had waited to update.