Last night I updated my Lumia 640 XL to 10.0.10586.420 and I wanted to make sure that it still worked with enpass. I tried to do a sync which failed so I uninstalled and re-installed. I still cannot sync or access any of my data stored on Dropbox. I also checked my Surface 3 tablet running 10586.318 and it can sync although it took a few tries. I tried on WiFi from the house and from a coffee shop so it's not a WiFi issue.
The message on my phone is: Not able to connect to Dropbox. Please check internet connectivity.
I can access the web, email, Facebook, Dropbox, Onedrive and every other web based service on my phone so WiFi is working just fine.