Erratic mouse functionality and USB

[Space Ghost]

This is a weird one, so I thought I'd make a report here.

I've recently acquired a new mouse. It's a Logitech M185, which is a very boring, standard wireless model. It operates using a similarly standard USB dongle, which is about 3/4 of an inch long and which I plugged into the USB port on the front of the desktop system. It operated fine and all was happy. Until it stopped doing that.

After while, the mouse began operating intermittently, jerking across the screen and becoming generally unable to be used. Occasionally it would operate normally, but without warning, it would become unable to center on any particular spot.

I started to diagnose the problem. CPU, swap, and other indicators were normal, before, during, and after the incidents. Driver was the standard HID for the device and no alternatives were indicated. Device was recognized normally - indeed, it had been working normally for days. Something must have changed. A read into the knowledgebase on this pointed to audio driver conflict or one of Windoze's "functionality" updates as possible culprits; still others said that moving their dongle to USB ports in the rear took care of the issue. A quick check of upgrades didn't show anything installed in the relevant timeframe...could it be USB? Nothing particularly changed on that front, either - except maybe...? It couldn't be that, could it?

And yeah, it was. The setup: there are four USB ports in the front of this desktop: two 2.0 on the left, two 3.0 on the right. The leftmost is an Asus Wi-Fi dongle, very slightly larger than the Logi dongle, which is plugged in next to it. I've saved the two 3.0s for data transfer devices...and sure enough, I'd plugged in my external backup drive to retrieve some archived files in the third port from the left. The drive is a SuperSpeed 3.0 Micro-B on the disk side, standard A plugged into the desktop, so it's about two inches long to the cable portion.

Now the keyboard also operates from the Logi dongle, so it was fine - as it was sitting directly in front of the system. But I'm right-handed, so the mouse was on the right side of the desk - shielded by a USB disk connector which was three times the size of the tiny Logi dongle and about an eighth of an inch to the right. After plunking my head down on the desk and getting an eyeline, I realized it was literally directly screening the mouse from working properly. Unplugged the disk and the problem went away. (I haven't yet moved the disk connector to the rightmost port to see if that would make a difference, but it might - that would give a better angle, at least if I used the mouse closer to the edge of the desk.

[Space Ghost]

Small update: moving the mouse to the left side of the desk also works, which pretty much confirms the original diagnosis.