Regarding this:
You may simply need to enable it in code as mentioned in this topic, for example in your setup function:
bristlefin.enableVbus();
bristlefin.enable5V();
// Wait for Vbus to stabilize before enabling Vout
vTaskDelay(pdMS_TO_TICKS(5));
bristlefin.enableVout();
If it turns out to be something else, please start that discussion as a new topic on the forum with a longer description of how you’re testing and what you observe.