Why did my market order in the pre-open session become a limit order?

As a general rule, all unmatched market orders in the pre-open will be carried over to the normal market as limit orders at the equilibrium price with their original time stamp. If the Opening-Price is not found, market orders will be carried forward at the previous day's Closing-Price.

In a normal scenario, a market order in the pre-open session should be executed at the best available price at the time the market opens. However, there are a few reasons why it might've been converted to a limit order:

1. Low liquidity: If there aren't a lot of buyers or sellers in the market at that time, your order may not have been able to be filled at the best price.