Written offer delay after verbal offer

After completing all rounds for a summer quant internship at an investment bank in NYC, I received a call from a recruiter 3 weeks ago, saying that they would like to extend an offer and provided some information regarding pay, benefits, and the team I will be working on. They also mentioned that I would receive my written offer "in a couple of days". I haven't received anything yet and I am getting worried.

I contacted the two recruiters about a week and a half ago to check in and they are ghosting me - not a single answer. On the other hand, my application status on WorkDay changed to "Offer in Process". I understand that these processes might take time, especially when a lot of approvals and signatures are involved, but if everything is okay (which might not be the case), why would they say "in a couple of days" and stress me out by ignoring my call and email? Is it common for banks to take this long to provide an offer letter?