Case fan speed drops to zero for just 1 SECOND then returns to normal

Here's a weird one that seems to happen at random times, maybe twice a day or so:

According to my Argus Monitor fan monitoring/control software, my computer's front case fan (PWM) is spinning along at a proper speed of about 340 rpm. Then Argus Monitor reports that fan rpm suddenly drops to ZERO in just ONE SECOND, and then fan speed is back to 340 rpm in the very next second. I caught this behavior in the act and looked at the fan, but the fan was spinning normally (I didn't see it slow down, let alone drop to zero). Besides, how can a spinning fan slow down to zero and spin back up to normal in just two seconds anyway?)

Could this be a problem with the fan, the motherboard, Windows 10, or Argus Monitor?

Windows 10 Home, 20H2, OS build 19042.1288

I would uninstall monitor and reinstall and see if acts the same