What are possible reasons for external keyboard input lag?

Solution 1:

The lagging sounds like wireless interference to me.

Many devices can be the culprit; wireless routers, displays, other Bluetooth and WiFi enabled devices, and even devices attached via USB 3.0 cables with poor shielding.

The closer you can get your USB dongle to the keyboard, and the further it can be from sources of interference, the better. A good USB extension cable might be what you need to take care of this issue.

Solution 2:

I had the same issues:

• Severe lag for keyboard/mouse
• Eventual complete disconnections

Apparently I fixed it by disabling handoff.

I read it somewhere but I cannot find it.

Solution 3:

I think it might be wireless interference. I have a pair of bluetooth headphones and the lag only seems to happen with the headphones are connected to the computer. I've had this keyboard and mouse combo for a couple of years and think the two are highly related.

I'm not sure how to resolve the issue though, but I will investigate some more and hope to provide updates in the future.