Hi Guys, having the same issue. Not sure where to look for a solution. Drag and drop just not works. With clicking an choosing from Drive or file on computer works, but not drag and drop.https://twitter.com/SlackHQ/status/668708259440820224 …
If you're using the app, make sure you're on the most up-to-date version. Could you please also clear your app cache: Help > Troubleshooting > Clear cache and restart? If that doesn't help, please write to us at feedback@slack.com so we can look into this. 
