Diagnosing why the left side of a print detaches from the board I have and Ender 3 Pro, which I'm enjoying except for an intractable problem. No matter how carefully I level the nozzle and tighten the X belt, using this great guide, the prints seem to be tilting to the right, particularly if they're tall. I realize this is a common problem, but I'm at a loss for what it's called and where the problem is most likely to be.

The first sign of trouble in paradise is that, after two layers of a simple rectangular base for a Galton Board I'm trying to build that uses sand, the right side is clearly thinner than the left:



This is with a translucent Overture PETG filament, 1.75&nbsp;mm.

For the board itself, which is about 15&nbsp;cm tall and looks MUCH better if printed vertically, I notice after about 3-4&nbsp;cm that the bottom of the left side is becoming detached from the bed:



This gets progressively worse as the print goes on:



The entire Galton Box takes six hours to print using the default PETG settings in Cura for a default level of detail, so I'd really prefer to find a way to diagnose the problem sooner. I know this is not a new problem, but I'd be grateful for any guidance on what it's called or links to how to fix it -- and how to determine if it's a hardware problem or not. 

Also, out of curiosity: If the machine isn't PERFECTLY level on the table -- my work desk appears to slant by about 2&deg; -- could that be implicated?
The uneven level is explained by the unfortunate choice of the printer manufacturer to not have a second Z lead screw. It is pretty difficult to level these printers, it is all a combination of the correct X belt tension and roller tension. The uneven level in the first picture is what is causing your print to detach, As can be seen you've got a lot of "squish" on the right side, but less adhesion (seen by the less transparent color) on the left, therefore it would fail on the left. 

You need to:


level better, 
fix the skew XZ gantry or 
use an adhesive (and/or a brim).




Please note that the level of the table top has nothing to do with the leveling of the printer, nor with the leaning of your prints. You're just having adhesion problems as a result of an uneven bed/gantry.