TLDR: batteries.

While air shipping is generally faster than sea and ground, several factors can cause unexpected delays.

Air shipping for items with batteries (such as electric skateboards) can be delayed due to limited flight availability. Lithium-ion batteries require strict compliance, and not all flights can carry them. If a flight is full, the shipment must wait for the next available one.

Additionally, during Chinese New Year, many shipping services in China shut down or operate with reduced capacity, further limiting available flights and causing congestion around that time of year.

These factors, along with customs inspections and airline restrictions, can all contribute to extended shipping times.