Root is required for this fix.
First, go to developer settings and enable Bluetooth hci Snoop log. Reboot. Then disable the Bluetooth hci log. Reboot.
Next, using a root file explorer (I used ES file explorer), navigate to /system/etc/Bluetooth/
Near the top is "BtSnoopConfigFromFile=false"
Change it to true, then make sure the following two lines are set to false.
Save the file and reboot.
After some browsing on the nextbit forums, someone had identified that the Bluetooth Snoop hci log was being written to the root directory of /sdcard/, causing significant battery drain. Their solution was to toggle the Bluetooth log on in developer settings, reboot, turn it off, then reboot again. It would always turn itself back on though. This prevents that.
(Bluetooth hci log is a file where android literally records all Bluetooth traffic information, which as you might imagine is CPU and I/o intensive. Normally used by devs for troubleshooting).
I decided to go back to stock due to constant bugs and freezes with the lineage 14.1 builds. Battery life has even been a little better on stock, with rock solid stability.
This prevents the battery drain aspect, but the battery settings still has a reporting error that attributes much more drain to Bluetooth than it should. I'm still getting 3-4hrs screen on time with lots of Bluetooth use after this fix. Better battery stats will provide accurate drain stats.