Test whether Briar is killed, loses connectivity, or is listed as power-intensive by power management apps such as the following:

https://play.google.com/store/apps/details?id=com.oasisfeng.greenify

https://play.google.com/store/apps/details?id=com.avast.android.batterysaver

https://play.google.com/store/apps/details?id=com.battery.power.batterysaver