How does thrust reverser selection have a destabilising effect on the rudder and increase the lateral skidding tendency of the aircraft?
This is called rudder blanking. While I was searching for it, I came across this image

(Source)
As the Skybrary article mentions

Rudder blanking is a particular risk to aircraft with rear mounted engines and &quot;T&quot; tails.

I emphasized the word particular since I perceive it as an indication that it's a risk for other planes as well without rear mounted engines.
Now the flow from trust reversers, disturbs the airflow around the rudder reducing its effectiveness. In strong crosswind you rely on rudder to keep the aircraft centered on the runway. If you apply thrust reversers right after touchdown, you reduce the effectiveness of the rudder and in turn it might reduce the crab angle making it harder to keep the aircraft centered.
Addendum
I will try to explain with a graphic, though as I've already stated in my comment, I'm not an expert.
As you can see in this image taken from Wikipedia, the thrust reverser output is not blocked by the wing, so it's quite safe to assume there is a jet similar to the first image.

I would estimate that the area of that vertical jet is more or less contained in the red circle seen in the next image. The free stream will push the turbulent jet from the reverser towards the back (as you can see in the first picture) and disturb the flow around the fin. The orange area is parallel to the free stream and shows the direction of the turbulent flow which might not be exactly the same in reality as the fluid particles have a tendency not to follow straight lines.
The plane is rotated 15 degrees to simulate a moderate &quot;crab angle&quot;. From the picture posted in GdD's answer, you can assume this can be more if the vertical wind component is high enough.

(Source of original image)
Now one thing you might need to consider is that the engines of a wing mounted engine plane have significantly more distance from the vertical stabilizer compared to the tail mounted engine plane. That distance might be able to weaken the effect of the stream, enough to not cause accidents like this mentioned by Sports Racer in his comment. But that doesn't mean the problem is not there, hence the warning from Airbus.