The issue is that when he triggered the clause on April 19th, we will have almost certainly paid some money to Leverkusen up front. So do we get that back now that the deal is void? We've presumably been paying his wages for the last month and a half, do we get that back too? When he became a Hull City player full time, his Leverkusen contract ended. If he "goes back to Leverkusen", then how would they contract him unless it's on some weird month to month deal (which would mean he would be valued less than the offer on the table).
This is the problem, the EFL state that they're doing this to help us be financially sustainable, yet every action they've taken represents the complete opposite.