BB S&T Sudden Additional Interview with Another Team after Verbal Offer?? Should I be worried??

About 2 weeks ago, the interviewers from final round gave me a verbal internship offer (BB S&T). I accepted the offer verbally right on spot.

But a few days after that I don't get any response from the HR, so I called up and checked. They said they were still in the process of selecting other candidates, and they wanted to send official packages all at the same time.

Still no response the week after, so I contacted again. Then they said they were waiting for the HQ for the final confirmation.

So basically nothing official (no package, no confirmation of offer form HR..) for 2 entire weeks since the verbal offer.

Then last friday, the HR suddenly sends an email saying they want me to conduct another interview with another team! So when I contacted the HR again, they were being rather vague saying that currently different desks were facing different hiring needs..

I conducted another interview yesterday and the interviewer didn't seem to be aware of the that I had received an offer already.. I didn't dare to ask the guy about the situation, and I also didn't ask the interviewer from final round because, well, I suspect their team might be undergoing some sort of restructuring..

What on earth do you guys think is going on? Btw, exactly the same thing happened to another guy from final round.. (we've been keeping in touch)