Perhaps this is no longer a kernel issue or at least no longer a regression. I am getting the same behavior with 4.14 and 4.13.11 and even the kernel from 17.04 . Normally when I am suspending at the end of the day I first close the laptop lid, then choose suspend from the menu on the external monitor... and that seems to work. Not sure how long the suspend menu has not worked with the laptop lid left open but today I still get it if I boot 17.04 from a different partition.
Perhaps this is no longer a kernel issue or at least no longer a regression. I am getting the same behavior with 4.14 and 4.13.11 and even the kernel from 17.04 . Normally when I am suspending at the end of the day I first close the laptop lid, then choose suspend from the menu on the external monitor... and that seems to work. Not sure how long the suspend menu has not worked with the laptop lid left open but today I still get it if I boot 17.04 from a different partition.