Leverkusen's problem comes from last season, it's in defense and Ten Hag is in a terrible situation because he found a team with defensive problems and he didn't make good signings to improve the defense, now he will be placed all the blame and rightly so, because he had time to choose other players for defense, now he will need to hold out until the next transfer window, I don't know until then what Leverkusen's position will be, but with this weak defense, I very much doubt that Leverkusen will be able to be in the top 4 places until December
I don't think Bayer Leverkusen's problem I mean the defensive problem you said started last season, it started this very season because as of last season they were ok only thing was that they couldn't find that consistency in them to meet up how they finished the season they won the league title, winning games became a problem and they could not withstand Bayern Munich that was really ready to reclaim what was theirs, no club was easy for them again.
This transfer window they sold almost all of their good players even their former manager Xabi Alonso left the side and ETH came in but could not make good use of what was left and today it seems like he's the problem and some will say is Manchester United bad luck that came with him, no...I feel the management are ok with the players they have and ETH should work with it. For now I don't see anything special happening at the club like no new addition will be made and if possible they have to play and win base on luck, the position they'll finish will be a shocking one if they don't improve the way they play with the players they have.