If you have updated to Platform Tools 25.0.4(you can check running android from command line) and it’s not working
Just download previous stable version e.g: https://dl.google.com/android/repository/platform-tools_r25.0.2-macosx.zip
Then go to your Android SDK home directory and replace platform-tools folder with the downloaded one.
Then do:
ps aux | grep 5037
kill -9 <pid of process of your incorrectly running adb>
And go
adb devices