my device shows briefly under adb devices then disappears

I got a (rooted) nexus 5 (with twrp custom recovery), and I develop on it using android studio 2.0. Recently when I type in adb devices, it shows my device for a couple of seconds then it vanishes! ie $ adb devices List of devices attached 03a3d66d0a4e64bd device $ adb devices List of devices attached 03a3d66d0a4e64bd device $ adb devices List of devices attached $ adb devices List of devices attached i tried everything: - changing usb port - adb kill-server then adb start-server - restarting phone - installing android 6.0.1 update.. any ideas? this is my adb version: $adb version Android Debug Bridge version 1.0.32 Revision 09a0d98bebce-android