I have no idea what
にこだわる means here.
The nuance is once day, my Japanese translator who suddenly switched to English (instead of Japanese like normal) to translate a question, and she submitted it to the Japanese client.
After that, I received above feedback from my client. My translator told me that the question was a little bit tricky to translate to Japanese, so she decided to go with English. It seems like the client was not happy with English there, so I guess the
にこだわる means something like
get stuck, doesn't it?