I am having the same issues even with the newer Kernel, 4.4.0-79-generic. Like others have mentioned above, I can mess with the settings and sometimes "it gets it" and other times it just causes the whole machine to lock up and I have to force reboot it. Even when the monitors do show up in xrandr - they are blank with the no signal screen. Messing with the settings becomes a 50/50 but even if it does "manage to find it", the moment you have to walk away, or the screen goes to sleep, its not coming back. Here is a screen shot of the error I get sometimes, other times, there is no error and the machine just locks.
I am also on a Dell E7250 Intel Core i5-5300 Intel HD Graphics 5500 Broadwell GT2 ** Attachment added: "Error message" https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1686189/+attachment/4891194/+files/Ubuntu_Monitor_Issue.png -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xorg in Ubuntu. https://bugs.launchpad.net/bugs/1686189 Title: External monitor connecting problem on Intel graphics card To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1686189/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp