Latitude 7480 and TB16 dock - laptop display and keyboard stopped working after undocking

I use my Latitude 7480 (i7, Win10 Pro, and TB3 option port) mainly with a Dell TB16 dock, external keyboard, mouse, and external Dell monitor, but also have need to use it stand-alone as a laptop, so being able to reliably dock and un-dock it is very important.

Today, after shutting down and disconnecting the TB3 dock cable, I tried to restart it via the power button next to the laptop's keypad, but it only flashed briefly, the laptop power button and the keyboard stayed dark, the laptop screen stayed black, however, the Windows start sound did play. I connected an external keyboard, mouse, and display directly to the 7480's ports, and then found the computer was on and working as if it was a desktop system. No amount of restarting will restore the laptop's keyboard or built-in display to operation when booting into Windows. Note: If I can hit "F2" at just the right time with an external keyboard, I can get it to go to the set-up menu and the laptop display then works as-expected (but only when viewing the set-up menu, booting into Windows keeps it dark).

I have researched this issue extensively, but it seems to be a common problem with this Dell hardware that lacks a good fix. To try to resolve this; I performed a clean install of Win10 Pro using the Dell Recovery software, ran the Dell Command update to get the basic drivers, confirmed the latest BIOS was installed to the Laptop and to the TB16 dock, reset the BIOS settings to factory default, made sure TB 3 was enabled, manually installed the remaining USB3, TB, and other driver updates in the order the online experts have advised is needed to fix the problem, and I made sure all TB3 settings allowed the dock to connect automatically without special permission. After this, the laptop worked fine, docked or undocked, without issues switching between the 2 modes ... for about a week that is!

A week or so later, the same problem came back ... I suspect that between Dell and MS, they installed some driver or OS updates that I can't undo via basic system restore point. The 7480 will run Win 10 using an external keyboard, mouse, and display, or if using the TB16 dock, but will not function again as a normal laptop.

I have no 3rd-party drivers or software installed, just Windows 10 Pro, MS Office 2016, and the various Dell utility software they install automatically, so this problem is either with MS or Dell or both. Many people have reported a similar issue, but I have not seen an actual fix posted ... is there a technical bulletin or software / BIOS patch from Dell or Microsoft to address this known and common problem? Thanks in advance for any ideas.