Via Amazon Seller Central News:
In July 2020, we announced ASIN-level quantity limits for products that are stored in our fulfillment network. We made this change to ensure that we can receive and store products for all sellers who use Fulfillment by Amazon (FBA).
We’ve heard your feedback, and are continuously improving our policies and programs to better receive and store your products.
Effective April 22, 2021, FBA products will no longer be subject to ASIN-level quantity limits. Instead, restock limits will be set at the storage-type level, offering you more flexibility in managing your shipments.