cyclist said:
it is not really "not a good thing" depends how you look at it. you are invited interview because they think your relationship is not genuine. but they didn't refuse your application so interview is your last chance to prove your relation is genuine. so that is a good thing that they give you that chance. no need to worry about it if you know your spouse well.
It's never a good thing when the office that is responsible for deciding whether to grant your spouse PR, believes your marriage might not genuine. That's really the only reason an interview is ever granted. Anything else, they would simply ask the applicant to submit more information or documentation, but something regarding the genuineness of a marriage, only an interview is done to address that. There are also many stories of people who went through the interview process, complain about how the interviewer would not even look at their presented documentation, become rude, and sort of already pre-determined that their marriage is not genuine even before asking any questions.
Just a few weeks ago, there was a sponsor who messaged me that his wife got refused at the interview, and the wife was really confused as to why, as she seemingly answered all questions well, and there aren't really any major red flags, they were both same age, had a long courtship, had a baby on the way, etc. There was one red flag however, and that was they had an argument before, so the sponsor withdrew the application, but then they made up and he re-applied. On his GCMS notes, the officer noted that they were compatible in every way, but had concerns about the withdrawal of the previous application, so they granted an interview for that reason.
Had he not withdrawn the app in the first place, they likely wouldn't have an interview, and she'd already be approved. Instead, you have a very compatible couple having to go through an interview, and were unlucky enough to be refused for some unknown reason. Some interviewers might have been in a bad mood, and that could affect the outcome of the interview.
So you can see, it's extremely important for any applicant to avoid the interview as much as possible. Even for a genuine couple, all it would take is one small slip up or a bad mood officer, and you end up with an unjustified refusal and unnecessary delays.