When hovering, my Mavic Pro is absolutely nailed to the sky, doesn’t budge. The Inspire on the other hand has a slight tendency to wander. Not a lot, but compared to the MP it doesn’t feel as ‘nailed’. Maybe they all do this? I’ve never seen another Inspire 1 to compare it with.
Anyway, two possible causes for the instability (for want of a less-powerful word):
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Old technology
– By this I mean the hardware (the VPS camera itself) and/or the firmware, which hasn’t been updated by DJI since July 2017 don’t forget. The firmware will be using (dated?) software algorithms to stabilise the drone, based on what it interprets in the downward facing camera. -
A faulty VPS module
– Unlikely, as it’s not throwing any errors or warnings, but it’s a sensitive component at the best of times, so you never know.
Well, as I can’t do anything about the stuff in # 1, I thought I’d try swapping out the VPS module for a new one, again because they’re only 1/4 the price they should be these days.
Here’s what the VPS module looks like on an Inspire 1, it’s mounted dead centre on the belly of the airframe.
Sideways on, you can see a small air vent here too.
Here’s the new one, it’s not much bigger than a matchbox.
DJI Spare Part No 39, ‘Vision Positioning Module’.
DJI definitely took some cues from Apple on their packaging 
Inside the box is the module itself and a silver foil pack containing a spare ribbon cable and three torx screws.
Interestingly, there is a ribbon cable already attached to the module in the box, so the one in the foil packet genuinely is a spare.
Off topic, I splashed out on some Draper precision torx screwdrivers. I’m fed up using cheap one-shot tools that disintegrate at the first sign of pressure.
For this job you only need a T6 driver:
Before doing anything you should disconnect the existing ribbon cable from the airframe. It’s the higher of the two connectors in this shot.
Which typically is buried deep inside the most awkward part of the airframe to access. You can see here I’ve actually removed the side frame-bracing arm to give me a bit more access:
Anyway, with the cable disconnected, you simply remove the three T6 screws holding the module in place and it all comes away in one unit.
Once removed, you can see a small rectangle shaped hole on the bottom, which your new cable will pass up through.
No more photos beyond this point as there’s nothing else to show really, it’s a very easy job to do.
The hardest part was plugging the ribbon cable connector back in to the airframe. You need some right angled needle nose pliers, or fingers the size of a 1 year old 
Still, it wouldn’t be a DJI product if it wasn’t bloody impossible to work on eh 