If it's stuck there for over a month, it's not normal. It may couldn't pass the check and returned. You need to contact the seller to reflect the problem and give you a solution as soon as possible.
My parcel: LV305930859CN has been showing up as “Wuhan City, Export Swaps Bureau retained 2021-10-21 10:12” for 10 days. I have messaged the seller via WhatsApp, and they said “Rest assured”. And “not to worry”. I asked “Has the parcel has left China yet?” , and the seller replied “Yes, flight departure”
If it's stuck there for over a month, it's not normal. It may couldn't pass the check and returned. You need to contact the seller to reflect the problem and give you a solution as soon as possible.