I'm using Lightroom CC on Windows 10 and having issues with Lightroom CC and Classic on the external monitor. The display issue is different, depending on which screen I open it on, but no matter which way I do it, there are problems. Thanks in advance for your help, I'm going crazy.
I have done some troubleshooting (below) and I have been trying to get support from Adobe for over a week, but they keep telling me someone will contact me and they never do (I've literally been on chat for over 3 hours today just trying to get a call scheduled). They have indicated this is a common problem for LR as it scales differently than the rest of the suite.
Running Lightroom on Windows 10 on HP Spectre 13", 4k resolution. Connected via display cable to Dell Monitor, 2k resolution. See below for screenshots of what's happening. System info at the end for reference.
Troubleshooting so far
In addition to checking the monitor settings and scaling, I have adjusted the high DPI settings and each change makes it worse.
I have done each of:
[X] Override high DPI scaling behavior. Scaling performed by:
I open the application on the laptop, and move it over to the monitor. It looks completely out of scale, and the work area is unusable.
I open the application on the external monitor. Most of it is normal, less the top bar (and anything clicked within it or popped out).
Scenario 2 (still)
After opening LR on the external monitor, if I bring it over to the laptop screen, it looks like this, everything incredibly zoomed out.
After DPI settings changes
Scaling performed by application
After changing the DPI scaling to application, the images were slightly out of focus (as if it still needed to finish loading). Cursors and small items were TINY on the laptop screen. Most was normal on the monitor.
Scaling performed by the system
After changing to system, it was still not focusing on the monitor, and then on the laptop, the image detached from the workspace, but there was no way to interact with it, along with two ribbons at the bottom.
By system, on monitor
By system, on laptop
Scaling performed by system (enhanced)
Similarly to when performed by system, it appeared to work fine on the monitor, but is misbehaving on the laptop.
I'm having similar issues with Classic (screenshot on monitor).
Detailed system info
Lightroom version: 3.1 [ 20191126-2330-434c343 ] (Nov 27 2019)
NGL Version: 18.104.22.168
Operating system: Windows 10
OS Version: 10.0 
Application architecture: x64
System architecture: x64
Computer model: HP HP Spectre x360 Convertible 13-ap0xxx / Intel(R) Core(TM) i7-8565U CPU @ 1.80GHz
Logical processor count: 8
Processor speed: 1.9 GHz
Built-in memory: 16121.8 MB
Real memory available to Lightroom: 16121.8 MB
Real memory used by Lightroom: 2492.8 MB (15.4%)
Virtual memory used by Lightroom: 2616.0 MB
Memory cache size: 2122.7 MB
Internal Camera Raw version: 12.1 [ 351 ]
Maximum thread count used by Camera Raw: 5
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Camera Raw virtual memory: 1259MB / 8060MB (15%)
Camera Raw real memory: 1260MB / 16121MB (7%)
System DPI setting: 240 DPI
Desktop composition enabled: Yes
Displays: 1) 3840x2160, 2) 1920x1080
Input types: Multitouch: Yes, Integrated touch: Yes, Integrated pen: Yes, External touch: No, External pen: No, Keyboard: Yes
Graphics Processor Info: DirectX: Intel(R) UHD Graphics 620 (22.214.171.12413)
Graphics Processor Detail: loaded: Yes, supported: Yes, compute: No, init: I2_GPU2, hard: fail_cached_sanity_test, soft: not_checked, wl: No, bl: No
OS Media Capability: true
Application Folder: C:\Program Files\Adobe\Adobe Lightroom CC
Settings Folder: C:\Users\jesse\AppData\Roaming\Adobe\Lightroom CC
Library Folder: C:\Users\jesse\AppData\Local\Adobe\Lightroom CC\Data
Display 1 (laptop) information
Display 2 (monitor) information
Adapter properties for display 2
Thank you. I have checked and am not sure that will help with how I use it, but I will try.
I did get a call finally from Adobe today and it's known issue, expected to be fixed in the next release (in about 60 days).
I have the same issue and it has been 60 days, did you get a resoultion and if so can you share it?
jessicae96188732 I have the exact same issue and am running the most recent versions of both LR Classic and PS. This forum and others I have searched over the last few days have revealed that this is evidently an issue that has been around for quite some time. Hopefully a solution will come soon. I'm curious if you ever got a resolution to this issue.
I Still have the same problem with Lightroom CC Version 4. Running a 4K SurfaceBook 2 and 2 External 2K Dell Monitors. Wish we would not have to pay for mediocre.
I'm having the exact same issue. My second screen is considerably larger. Having to open it on my second screen if I want to edit but even then the menu bar is huge.
Thanks for the well researched post Jess. Second monitor with LR Classic has been buggy for me with Windows 10 and multiple monitors as long as I can remember. The exact symptoms vary but it is always unstable, often unusable. Forget about full screen, I've given up on that. Typically it either disappears completely or more often jumps to a different monitor and absulutely refuses to go where I want it. Last upgrade made it worse. It's frustrating paying a monthly fee to Adobe and getting no support for this longstanding critical issue. For example, (expletive deleted) on Adobe chat once suggested "drag and place it where you want it" 😞 Anyway, hope you find a solution - I will try the suggestions here and see if anything works.