Exact same time every night Eufy wired doorbell/cam triggers and a bright light comes on for a few seconds. Nothing is triggering physically, similar view Eufy cam does not detect anything either. No ambient light changes seen from any camera. Just a few second long burst of light, starts dark a few seconds- then light burst for a few - then dark view for remainder of 20 second interval. Timing is very consistent.
I have seen this when I have two indoor devices looking at the same area. My indoor cam and pan & tilt cam in my shop can see each other. At night, usually at 4:27 AM about 5 nights a week, the pan & tilt cam does a 360 and checks for updates. That sets off the motion detection on the indoor cam.
Have also seen this in the backyard where one cam will detect motion and turn on its IR LEDs, which triggers the other cam to wake up and record basically nothing but the first cam waking up.