@MEB
Thanks for the welcome!
Well, in fact I do run a clipboard manager. Good call. I use Clipboard Help & Spell. I disabled it (actually exited the app altogether) and tried again, but still got the ctd. That got me thinking about all the errors Excel throws whenever I try to copy something. The copies in Excel always work, but always throws a "picture too large" error, which has to be dismissed before I can continue what I'm doing. Frustrating. I digress.
All of that got me thinking about Windows 10's new clipboard history feature. So I checked and it was ON. So I turned it OFF. Affinity Designer was then able to copy without crashing.
So then I turned CH&S back on, and AD went back to crashing again. CH&S has an application white/black list, so I set it to ignore Designer.exe (and crashpad_handler.exe also). Still crashed. I cannot explain that. I will contact the author of CH&S for verification that his ignore list is actually working, or for his thoughts on why, when set to ignore an app, it is still interacting with it in some way.
So for now let's just forget about CH&S. I exited the program completely, then went back to testing only with the new Windows 10 Clipboard History feature. When ON, Designer.exe crashes. When OFF, it copies fine and does not crash. So if Serif can fix whatever the issue is causing the crash with Clipboard History, I'm going to cross my fingers that it fixes all other clipboard managers, too.