Macbook Pro 2015 Lid seemingly overnight stopped from closing properly
The most obvious diagnosis at this time would be a swollen battery.
A swollen battery can cause different symptoms from a misaligned track pad to a malformed keyboard.  In your case, it appears it's mis-aligning the case causing the lid to not close properly.

Why is my Early 2014 MacBook Air&#39;s Trackpad Uneven?
Stiff trackpad on Macbook air
Macbook Pro mid-2015 15&quot; swollen battery

A battery swells because the off gasses that are normally vented are trapped (see the first link for more info); the battery swells like a balloon.  Suffice to say, this is more than an inconvenience, this can cause something called &quot;thermal runaway&quot; where it could cause a fire.
I strongly suggest that you get this addressed as quickly as possible.  It's impossible to predict if/when this could occur, but it is very dangerous.  You cannot put out a thermal runaway fire as the chemical reaction will continue.  This is why firefighters simply allow hybrid and electric cars to burn out; they will try to contain the fire, but they cannot extinguish it.
At a minimum, from a non-safety point of view, the battery is warping the aluminum structure - it could be permanently be bent, or unlike it's counterpart steel, will tear once it reaches a certain point.