They looks to be Thermal Relief pads to aid in manufacturability.
From some searches:
- Thermal Relief Design Guide for Your PCB for Altium
- PCB Thermal Relief Guidelines for Effective Layouts for Cadance
Relevant part from the Altium article:
A thermal relief pad provides a way to keep heat confined to a pad for mounting a component to a printed circuit board with solder. The pad for a component normally peaks through the solder mask, allowing solder to be placed on the pad during assembly. Some copper is removed from the edge of a thermal relief pad, allowing heat to be confined in the pad when applying solder during assembly.