It's one thing not getting back to potential candidates who apply for a job and don't make it past the resume screening process -whom ironically get notified via their automated rejection system actually-, and others who not only make it past the phone interview but reach all the way to the 2nd in-person interview and then getting completely ghosted! It's not only unprofessional and disrespectful, but it also sends a bad impression about your company even if that's not the case. I understand that sometimes, you don't have the answers or your waiting on the hiring manager to make up their mind; however, a simple acknowledgement of the follow up email and a quick update should be more than enough; but to completely stop replying or answering phone calls is very unprofessional and waste of the candidates time; especially when that candidate takes the time to prepare and travel to your site more than one time over a period of more than 2 months!
Now for all fairness, the people I have met with were very nice and welcoming. I think the hiring process itself needs improvement...