IA Collaborative interview questions

2 rounds, 1st round 1 interviewer (HR), mostly behavioral + brief introducing your background, 2nd round 2 interviewers (department head), you need to make a 10-page deck to walk them through a case you did in your previous job

I interviewed late December. Applied through a referral and received a pretty positive response, the interviewer mentioned I was top of the consideration and our conversation went well where I was able to showcase some of my past projects I had developed / prototyped in the AI space. My conversation went well and the hiring manager shared a keen interest throughout the call and told me to wait until early January for a follow-up interview. However, on first week of January, I received an regular rejection email without listing the reasons. This seemed super confusing, especially after leading me on and expressing a keen desire to explore the next stage of the process with my candidacy.