Leverkusen as a whole have been in awful form and have provided zero service to him and the other strikers on the team these last few weeks. Injuries have been extremely disruptive to them.
In particular, losing winger Karim Bellarabi at the start of the season was devastating. He, along with Hernandez, is their best player, and those two have a great understanding.
The good news is that he's due back after the winter break. The goals for Hernandez will start flowing again soon enough. He hasn't been "figured out."
Ffs, the boy's a great striker, but gets zero respect more often than not.