The interviewer is late and ill-prepared
I was stood up for the phone interview twice by a manager. I had the feeling that he conducted the interview since he had to and it was not his job. The technical questions asked during the interview have little to do with the job spec requirements.
Companies tend to treat candidates with more care than actual employees, this manager doesn’t have time to conduct a proper interview, he probably won’t have time to give you thorough training and regular feedback once you’re hired.
By the same token, since the interview keeps getting delayed, it usually means the company is undergoing massive changes and the job in the posting might not be the one I’d actually get. Worse, it may be an indication that the ship is sinking, thus making it one of the more alarming signs I don’t want the job.