Probably just an ego thing after he said he wants to win titles with Barca and handing in a transfer request just weeks later. PSG also sent that formal letter of August. Barca is not in a hurry, but won't change that the transfer will happen.
It would seem like Barca is trying to get more than 25m from the deal (so there could be some truth in the story of Barca kindly asking Dembele's camp to give more percentage of the transfer fee to them).
So Dembele's camp refused and Barca seems to be legally able to stall this till 21st August, so we release the needed documents quickly if Dembele's camp responds to their request.
Now Dembele is also strong-willed, like when he refused to be used in the transfer window as an exchange for Neymar years ago or when he was willing to seat on the bench and leave for free so it'll be interesting to see who wins, and maybe Xavi letting Dembele train with the squad is a sign of goodwill to see if Dembele have a change of heart and advise his camp to give more percentage to Barca to fasten his exit.
The best thing IMO is for this to end quickly, cause the drama is too long and unnecessary for an added 10m or less.