Precision 7740: screen and keyboard backlight glitching when not docked

When my new Precision 7740 is attached to its WD19DC dock, everything is working well.  No glitching, no issues.  The dock is connected to 2 additional external displays (each via DisplayPort), and an external keyboard and mouse.

When I unplug the laptop from the dock and try to use it standalone, two strange behaviors manifest:

1. The laptop's screen starts to glitch periodically (every few to a couple dozen seconds), as if it temporarily loses and then regains signal.  This sort of 'blinking' and 'flashing' is really obnoxious and disruptive, though it doesn't appear to otherwise interfere with proper functioning of any software (at least, not that I can tell...)
2. If I let the laptop sit idle for a while, and if I have the keyboard backlight enabled, the keyboard backlight begins to automagically turns itself on, then off, then after a while back on, then eventually off again, and so on ad infinitum - without me touching the keyboard or otherwise disturbing the laptop in any way.

In case it matters, the screen on the laptop is 4K, set to 2560x1440 resolution at 60 Hz, and is being driven by AMD Radeon Pro WX 3200 graphics card, with the Intel iGPU disabled in the BIOS.

Given that neither of these symptoms manifests while docked, I suspect that the issue is somewhere in the Thunderbolt drivers and/or related docking or screen/peripheral-device management stack: it's as if, while undocked, the laptop is continuously trying to re-establish its connection with the dock and failing to do so (because no Thunderbolt cables are actually plugged in.)  Anyway, that's the hunch I have about it - maybe I'm completely wrong....

Oh, one other weird symptom, which may or may not be related to the above.  This one, I've only seen manifest while actually docked:

• When I lock the computer and leave it sitting there for a while, the main screen (which is the only one not blacked out; displaying the lock screen) occasionally switches off (goes dark) for a few seconds, then switches back on (still showing the lock screen), then after a while switches off again, and then comes on again, and so on until the laptop eventually goes into proper sleep mode (per my power plan settings.)

In case it matters, I have my power plan set to DELL's 'Optimized' profile...

Edit to add: all of my drivers and firmware are fully up to date; I'm running Windows 10 Pro 64-bit version 1903 (OS build 18362.418); Dell SupportAssist indicates no hardware issues and no pending software updates at this time.