Energy Impact Center interview questions

Was initially contacted by the Energy Impact Center in-house recruiting team on LinkedIn looking for an I&C Engineer. Had a 30 minute phone call interview with them, where we discussed the role, company and mission A week later I had a 30 minute video interview with a senior member of the Engineering team about the role, going more in depth to engineering and my qualifications, problem solving skills After the second interview, I was sent a technical problem to solve and given a week to solve and send back my answers. After completing and submitting within the time frame, I heard nothing, not even a confirmation that they had received my submission. I reached out after a week to make sure, and received a nice response (Holiday season, very busy) and they verbally set up a meeting for the following week. On the day of the meeting I reached out to make sure, since I hadn't received a meeting invitation or time, received a nice response (want another employee to sit in on the next interview, they're not available for another week), I told them fine, and to please contact me when they can both get together. I have still not heard and it has been over a month. Ghosting a candidate that you initially reached out to, after they spent a week of their own free time on a technical interview is unprofessional, at best.

The interview process consisted of a phone screen with a recruiter, two video interviews with managers (including the founder), a position-specific assignment, and in person interview in their DC office.