a2dp sink: Can't get volume change events

[avasilev]

When running the IDF a2dp sink example app (IDF version 5.3), when changing the volume from my phone (Xiaomi Mi8), the ESP doesn't get any ESP_AVRC_TG_SET_ABSOLUTE_VOLUME_CMD_EVT notification. The phone has absolute volume notifications enabled in developer settings. In fact, the target event callback doesn't even get ESP_AVRC_TG_CONNECTION_STATE_EVT, nor any other events besides ESP_AVRC_TG_REGISTER_NOTIFICATION_EVT with ESP_AVRC_RN_VOLUME_CHANGE (phone subscribed to sink-initiated volume change notifications). The CT callback does get all expected events. Enabling verbose logging of everything also doesn't show anything happening when I press the volume buttons on the phone. The phone does change the volume by itself, but reaches a relatively small max gain. For comparison, I have tested the same phone with a bluetooth speaker, and it does change the volume with a large gain. Am I missing something?