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's Trackpad Uneven?
• Stiff trackpad on Macbook air
• Macbook Pro mid-2015 15" 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 "thermal runaway" 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.