DOL: The Daily Order Limitation is the maximum number of orders you can          receive on a daily basis. Once this limit reached, your shop will not appear online until the next day. The initial limitation number is 5 for a new seller.

PSOL: The Pending to Shipped Order Limitation is the maximum   number of       orders which can be under “Pending" status simultaneously on your Seller        Account. Once this limit reached, your shop will not  appear online until you ship at least 1 order.  The initial limitation number is 10 for a new seller.

If your shop was under volume limitation then it may due to below reason

The ratio of OOS is high-Once your cancellation rate over than limitation,your shop or  your products will be offline.

The return rate is high- Once your order returned(quality issue) rate over than limitation ,your shop or your products will be offline.