Amber light blinking on AirPods case

I have the AirPods Pro gen 2. When I plug in a USB-C cable into the case to charge it, the light on the case blinks amber for a few seconds, then goes out. After googling why the amber light blinks, I have reset the AirPods, used “Forget this device” in the Bluetooth settings of my iPad and iPhone, restarted the iPad and iPhone, and re-paired the AirPods, but the case still blinks amber for a few seconds when I plug in the charging cable. Note that the case and AirPods are charging. What’s wrong?