We don't know the exact details of the Heading 1 charges so can't be sure. But with the explicit mention of related parties, it's a fair guess that they're challenging our view that Etihad and the other AD sponsors aren't related parties. Even in the worst case scenario, which is highly unlikely, where the tribunal finds that Etihad was a related party, that's only a technical financial reporting issue at worst, so no one is going to lose any sleep (or points) over that.
I suspect they may also be going back over the UEFA/CAS ground of misreporting shareholder investment as revenue, which would be bizarre if so. If that were the case then we could be found to have over-reported revenue, which is potentially serious. it unless they've found some previously undiscovered smoking gun to support that case, they'll struggle badly to land it. And if they had found that smoking gun, they'll struggle badly to land that. And if they had found that smoking gun, this would likely have been done and dusted long ago.