Netflix had some great quotes about this from their earnings and specifically called out Kantar's data would show less viewers in the short term.

They had noted they saw or expected the users who were on someone else's account and who used it actively to come back with their own accounts or convince the account holder to pay for them

I did more of a write up based on what they are shared in their earnings here: https://upollo.ai/blog/learning-from-netflixs-earnings