LCD Display backlight issue, Can be seen by dropping a torch

Your problem is a ribbon cable connection of the LED backlight circuit. Here’s a photo explaining the connections:

Photo credit: @just1ed www.macplus.sg

If you can you could try cleaning the connection surfaces and reconnect the connector. Using 85% or better isopropyl alcohol on a cotton swab (Q-Tip) wipe the gold contacts.

Here’s the guide you’ll need to follow to pull the bottom cover MacBook Pro 13" Function Keys Late 2016 Lower Case Replacement And yes, this is for a different model than yours it’s the same procedure!

If that doesn’t work you’ll need a new display assembly as the cable its self has a tendency to fail. Apple had been getting a lot of cable failures in all of the new 2016 thru 2017 models. Both the 13 & 15” models share the same display design. Sadly, the cabled are mounted permanently to the display and can’t be replaced on their own.

If you can, on one of your travels get to a real Apple Store and let them fix it so you have a proper record of the repair as I do believe Apple will be offering a rebate for people who had the display replaced. You might even try getting then to post a warranty exception as this is so common a failure and then it would be a free repair. Sorry to say the display is that expensive ;-{

Don’t forget the sticking keyboard issue this system also has is currently being covered under an extended warranty program Keyboard Service Program for MacBook and MacBook Pro