Suspend/resume problem (Skylake-based system)

[Robert Kopp]

I am using FreeBSD 12.2 (x64) on a desktop system, with an i9-7940X processor, ASUS TUF X299 board, and Nvidia GTX 970 GPU. The GPU is using the nvidia-driver port with ACPI support, and a generic kernel.
If I just ignore the computer for a while, apart from observing what it does, the screen turns off after 10 minutes (as I requested). After another 10 minutes, the screen turns back on briefly, with a notification that the system is about to suspend. However, there is a little hard drive activity for another five minutes or so before this activity is extinguished. At that point the power light remains on steadily (should be blinking, as it does when Windows or Linux is suspended on the same hardware). The computer cannot be resumed with the keyboard, mouse, or power switch, and a hard reset is needed. (The mouse is wireless, but it awakens the other two types of OS.)
Since this is a desktop system, it would be acceptable to use it without power management, although such efforts have been met with "panic: running without device atpic requires local APIC." Or if it is going to suspend improperly, it should happen after the computer has been idle for about an hour, so that it never does actually suspend. It is possible that my hardware is just not fully compatible with FreeBSD, but if it is I'd like to solve the problem.