I have this exact same problem - 2018 MBP, Dell U3415W. Sometimes it works, sometimes I can move the mouse enough to get it to work, sometimes the monitor won't wake up at all, sometimes the monitor wakes up and has a VGA screen resolution. I thought I had "fixed" it by turning off sleep mode in the MBP, but after a couple of days of working properly it started failing to wake up again.
I know its a problem with the macOS somewhere but Apple just doesn't seem to be focused on fixing these types of things. Even if you file a bug report it disappears into the ether and is never heard from again.
Re:Apple of 2019 is the Linux of 2000
by terinjokes on Monday October 14, 2019 @08:19PM
(#21254314)
I own a Dell P2715Q 4K monitor and was having similar issues across operating systems. My understanding is Dell silently fixed this in firmware on new units, but provides no way of updating the firmware in the field.
Re:Apple of 2019 is the Linux of 2000
by someguydave on Monday October 14, 2019 @10:08AM
(#21248421)
Yeah I have similar problems with a Dell 4K Monitor and a 2018 MacBook. I have to power cycle the monitor to get it to work on occasion.
Re:Apple of 2019 is the Linux of 2000
by around_here on Wednesday October 16, 2019 @08:10PM
(#21277588)
I have the same issue, but I'm also using the Dell 180w dock with it. I just have to switch ports for the USB-C cable that comes from the dock 1-4 times. Usually the first plug in produces nothing on the monitor. The first port swap gets me on the external display, but at 1920x1080 resolution. The 2nd port swap gets me back at 4k on the external.
- Switch the USB-C port from one to another - Open up my laptop from clamshell mode and switch the cables around - Unplug my monitor - Restart my computer
The nuclear option of rebooting my computer and monitor always seems to work.