Trent has speed and when in counter-attack mode he is very good at piercing the right side of the opponent's defense, this is one of his advantages and that's why Real Madrid wants him but his weakness when in defense he is not strong enough sometimes he loses his position and is not consistent enough in defensive transitions but I think Xabi can overcome this weakness and one example is implementing 4 defenders as a cover to cover his shortcomings, in 2 matches Xabi has not been successful enough but I am sure that over time and the chemistry between Trent and his defense partners is well established this will work.
That is how Liverpool used him for many many years, so it would be difficult for him to adjust overnight. Give him some time and he will get used to it, or maybe he won't and he will stay a bad defender but they will use him as wing back more often and that would mean defense would be ready for anything that comes from that side.
It is not really that shocking for any of the players to just see their wing back be up ahead, and not ready to help on defense right away. The difference between Trent and Huijsen is that Huijsen is a defender, pure defender and that's it, but Trent is someone who is a wing back and that could be the most important difference. If they can do that, then we are going to see this thing change a lot with time. Trent just needs to be utilized for who he is, and how he plays.