The Telegraph claim to have seen the detailed judgement from FIFA's Player Status Committee ruling in favour of Nantes and against Cardiff in the dispute. They also claim that a 3 window transfer ban will hit the club if it doesn't comply with the ruling:

https://www.telegraph.co.uk/football...n-fail-comply/

If this is accurate it explains more of the reasons for the FIFA decision, although it leaves a load of questions and issues that form the basis of the appeal to the Court of Arbitration for Sport. English and Welsh law vs French law is one of them; another is the Cardiff case that Nantes (through the McKays, one of whom was on their payroll) are responsible for the tragedy and liable for the financial losses that followed.

It doesn't get any less ugly - treating human beings as assets and commodities. It may suggest, though, that Cardiff will have to pay up to Nantes and argue the legal toss after in an attempt to recover the payments.