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.
What is clear is that at this time Mane position is still irreplaceable, Diaz and Nunez are still beyond expectations, that Liverpool still need aggressive players and have attacking instincts as well as being proficient in assists. Look at Nunez performance at the World Cup, just as he can't give his best. It still takes time for Nunez maybe 2 to 3 years he will be greater. But for now Liverpool needs a new player who can collaborate with Moh Salah on the front lines. Because Liverpool's attack structure is still ineffective.
Sadio Mane's position might seem irreplaceable because truly his departure from the club was premature and could have been avoided by the management. Its left for the new players to do their best to improve the squad and help the team get good results in their games so far. I suggest more signings in the January window to strengthen the team and boost options in vital positions. Liverpool are currently lacking quality in the team and need to make more signings.