It can be an alarming sign, that is true, but the chances are great that this is an ordinary change in the recruiters’ plans. One of the interviewers is out of town or has to participate in another important meeting. The team has to focus on more important things than interviews or needs to finalize some project asap.
When you get the news that your interview is rescheduled, react calmly, and confidently. Your task is to find out when the interview will take place and to show that you are still interested in the position. Thank the recruiter for letting you know about the changes beforehand and promise to come when planned.