How to know what is causing a cursor lag on Mac?

I have disabled the Handoff feature on my iOS device - and the lag has disappeared.

As the cause can be both hardware and software related, different measures have to be taken to examine the root cause of your cursor lag.

Hardware

Seeing as your issue affects several peripherals, it is less likely that they are defective. It is however recommended to try to connect them to a different computer to exclude this as a possible cause.

There does exist a problem with radio interference when using 2.4 GHz devices (Logitech Unifying Receiver / Bluetooth) along with a USB 3.x peripheral connected to the computer. This interference is known to cause significant lag in the mouse response. I would begin by investigating if this issue applies to you before moving on to other sources. Simply identify if any USB 3.x peripherals are connected. If so, disconnect them and consider if the cursor movement changes. The USB 3.x issue causes erratic behavior in the cursor which should then be gone.

Software

Look into conflicting applications. Disable all non-essential running applications - especially those directly affecting the cursor such as SmoothScroll, Scroll Reverser, Steelseries ExactMouse Tool, Steermouse, BetterTouchTool and so forth. Evaluate if the issue is resolved by disabling the applications. If this is the case, reactivate them one by one to find the exact culprit. The problem could be associated with two applications in conflict, as the Apple macOS APIs can respond differently when two apps use them simultaneously.

To further evaluate the cause of the issue one can use applications such as iStat Menus to look for usage spikes related to the lags. Further analyses will have to be done.

I had the same issues when moving the USB dongle to the other side of the Mac Book so that the Mac Book was in between the dongle and the mouse. As soon as I moved the dongle closer to the mouse and connected it into a docking station with nothing in between dongle and mouse, lag was gone.

I had these issues when I plugged in just the USB 3 cable to my recently acquired Mac Mini 2014 and had the cable across the unit, when I unplugged them or moved them to the side the jitter went away. even worse I had a dual dock next to the Mini and it destroyed the b-tree node on all the hard drives (x4) I put in there, so I couldn't mount them anywhere after that, moved the dock away and it's working fine so far.