Cambridge Design Partnership Graduate Manufacturing Engineer interview questions

After shortlisting of CV, had an online technical interview followed by in-person technical interview. The online interview only had one interviewer and the in-person round was 3 hour interview with 3 interviewers.

Was invited to an online interview with back to back 2 x 1 hour sessions with different people. They both asked essentially the same questions about cv and then technical questions about some of the products they have. The role was manufacturing but I dont think either interviewer knew this, however they were very friendly. Was asked more about product design (which is a function of the position) but nothing on manufacturing really. I was told there would be a member from HR joining the call afterwards for 30 minutes but nobody joined. Rang the office and they said that they would call back within the next day. Never received a call back and was told the next day that i wasn't successful because my technical answers lacked depth. Asked for more feedback and receieved nothing. When told i was invited to interview it took 1 month for them to reply to my availability email. Tried calling but was told the HR member was going into a meeting and would call back. Never receieved a call. Poor communication as a whole.