My problem was more or less from the beginning -- I got the laptop (GX502GV), ran all the updates (Windows, NVidia, Asus), and almost immediately had problems resuming from sleep. I have not tried safe mode or restoring the OS, because it only happens intermittently and is not quite annoying enough to go through hours of troubleshooting. (That's also why I haven't tried to contact Asus about it yet.)
Now, for the last few weeks, I haven't had the problem. I made a few tweaks to power settings, and disabled "Allow this device to wake the computer" for the NVidia USB-C device as described previously. I think Armoury Crate updated a week ago through the Windows Store?
I also noticed at one point that I was seeing freezes / spontaneous reboots a few seconds after plugging in the power adapter. Coincidentally, it was very common for me to plug in the power just around the same time I was resuming from sleep -- I'd pick up the laptop, open it, turn it on, then get the plug and hook it up. So, I started turning it on and waiting until I was at a stable desktop for a minute or so, *then* plugging in to power. Since I started doing that I don't think I've had any freezing during resume / boot. It could be my "superstition" about not attaching the power adapter until the system is finished resuming, or it could be one of the device settings I changed, or a software update, or some combination of the three.