The reason why Liverpool's form dropped this much should be some mental problems. Of course they faced some injuries and had many missing players as a result. Diaz was one of them and we all know how important he is for the team now. He is trying to do his best to fill Mane's place in the team. His performance so far has already been impressive.
I think that liverpool didn't get mental problem. It can win against a big team. That proves that if the mental from liverpool was still good at this moment. The problem is when it comes to the inconsistent performance. Liverpool has capability to win against any big team in EPL but sometime it has a very bad performance during the match against the big club.
I think that liverpool didn't have mental problem for sure. the only problem that faced by liverpool was inconsistentcy with its performance.
However I don't think injury is not the main reason for this. Because they had really bad games in which they defended their opponents very poorly. Klopp needs to help the players improve their motivation. This squad are capable of doing anything they want. They just need some push.
Liverpool has so many great players that can substitute the injured players and how can you think that was badly affecting the performance from liverpool? liverpool already prepared some new players to be bought and this to make sure the squads has some great players to be used.