@dhgutteridge: Thanks for the quick response. After running all night my system finally hung again. I ran "journalctl -k -b 0" via ssh as you suggested, but no new entries whatsoever appeared since yesterday evening. I have emailed a file dump from that command to you, in case there's any thing unusual in it. I have also attached a /var/log/Xorg.0 to the email to give you details of my Nvidia video hardware.
I am not using any suspend/hibernate functionality at all. This is a desktop computer and I am only using simple "Screen Energy Saving" under KDE system settings. I do not invoke "Suspend Session" at all (left unchecked).
Sorry for the blank comment above; just figuring out how to add comment properly.
Exact same problem as anonymous above: Fedora 25 stock 4.10.8 kernel and all earlier 4.10.x kernels. Total display lockup on KDE plasma when screen saver kicks in; intermittent: happens about every 3 - 5 times, otherwise normal screensaver. Can ssh in, but normal shutdown stalls after "shutdown now" command; only forced power cycle recovers. Have not found nouveau errors in logs but I may not know where to look. Have checked /var/log/messages and dmesg. Happy to test patched kernels.
Thanks for your ongoing great work!