It is just the nature of Wavetrac's design how their diff will work without load on one wheel
Wasn't my car but I first noticed it in the passenger seat it doesn't ever lock both sides together it just sends power left to right to left to right etc etc all the while the steering wheel getting pulled as the power was transferred
Hmm.. interesting. The Wavetrac LSD isn't a locking differential so I don't expect it to lock both sides ever and I think that is intended. However, I was speaking with Wavetrac and they say that it shouldn't be shifting power left and right repeatedly like that. Putting power down to any said wheel and transition between wheels should be smooth and the steering will shouldn't be jerking around.
Has your friend talked with Wavetrac? I'm quite confident that they would try to help your friend out with the situation, especially if the LSD is defected.
We actually had one of our Porsche customers receive a diff that wasn't working correctly. Wavetrac fixed that owner's problems at no additional cost to said owner. They are more than willing to help their customer if the customer is willing to work with them.
I am still very confident about Wavetrac and my mk6 GTI will have one installed shortly too.