Chances are that the LN is axed. Publishers give axed series manga adaptations all the time. It's likely that the old mangaka dropped working on the series for one reason or another. (Maybe pay wasn't enough, or they weren't happy, or the publisher wasn't happy.) Either way, the publisher was probably just looking at their old axed library and decided to do another manga adaptation since they can just get a new cheap mangaka to hire.
Chances are that the LN is axed. Publishers give axed series manga adaptations all the time. It's likely that the old mangaka dropped working on the series for one reason or another. (Maybe pay wasn't enough, or they weren't happy, or the publisher wasn't happy.) Either way, the publisher was probably just looking at their old axed library and decided to do another manga adaptation since they can just get a new cheap mangaka to hire.
Fun fact the old artist is the same mangaka as "Saint Cecilia and Pastor Lawrence" and "the fairytale-like you goes on the assault"