In Reddit I found a few more people having similar problems for two months now, and I am not new in Bitstamp, I have been using it since 2018. I also asked them if it could be a problem with the ID, or probe of address, and they told me that the documents and ID are good, so this is not a KYC problem.
Maybe they didn't block withdrawals for everybody but it looks like I am not the only one having problems there, and the most worrying is that there is no explanation after so long.
Custodial exchanges can be triggered happy with their KYC/AML policies hence a few more people are bound to get hassled. This is why even with established exchanges, it can still be risky. Also, if they haven't finished looking into you case, there's a good chance it's an open ended answer.
I would suggest following up your case on their social media as well. For instance:
https://twitter.com/Bitstamp/ -- check bio. Be aware that there are loads of scammers pretending to be bitstamp so always triple check.