XPS15 9570 screen blinks every 15 seconds due to wifi card

I previously had a problem with screen blinking on my 9570, which I eventually traced to the Killer wifi card--disabling the card resolved the problem. I replaced it with an Intel AC9260 card, and all was fine...for about 6 months.

Now the problem is back. The screen flashes for about 0.5 seconds, exactly every 15 seconds. I've noticed the "wait" cursor appears briefly beforehand, and there is a brief spike in CPU and GPU usage, seen in the task manager performance tab. If I disable the Intel graphics adapter, the blinking still happens, but the GPU spike occurs with the nVidia graphics adapter.

If I disable the Intel wifi card, it goes away. I've uninstalled/reinstalled/updated the drivers for the wifi card and the display adapter, as well as updating the BIOS, without solving it. I thought about system restore, but the oldest point available is from 4 days ago, and the problem developed a week ago.

Has anyone else seen this happen? Any suggestions?

EDIT: I've found that it's not disabling the wifi card that fixes it, it's disconnecting from wifi.  That is, I can leave the card enabled but have no wifi connection, and the blinking stops.