Q. After having passed my selection interview with a visa official, I was requested to attend a second interview. What is this interview for?

Answer: In cases where a second interview is requested, it is not typically for the purpose of selection, but rather a matter of security (which may be requested in the event that your profession fell in certain fields; i.e., nuclear physicists).

Assuming that there are no grounds by which you may be deemed to be a security threat, this should not affect your chances of obtaining PR status, and would delay the application to the extent of the duration until the second interview.