MacBook Pro 2017 13 - black lines on the bottom of display

The Apple discussion space allows the collective Mac population to have a place to discuss things. Sadly, Apple tends to yank technical issues (as well as the people with proper answer) like yours as it brings quality questions out into the public space. The people who know what’s truly going on are not there! They are here!

So lets first define your issue: This is a scan issue within the display. This is not a cable issue so replacing any won’t fix this. FlexGate is when the backlight LED’s loose power giving a stage-lighting effect

So what is this scan issue?? Apple altered the display design so part of the displays logic is placed within the main case so Intel CPU heaters! Kills the T-CON logic.

Sadly, you need a new display assembly to fix this and to prevent it from happening again get this app TG Pro so you can monitor your systems thermals (and push it if needed).

I also recommend you clean the dust and debris out of your systems fans and heat sink fins so your system is getting the needed cooling, and lastly don’t block the vents! Don’t use your system on a bed or rug which suffocate your systems vents.