Hi Py0_,
The Master branch is the “bleeding edge” of the Engine development. Updates and fixes are added into it as they are completed and the Engine as a whole may not have been fully tested with the updates in place. As a result, it can be potentially unstable, may not build at all, and is essentially a “use at your own risk” version of the Engine.
What you would typically want to do if a fix to an issue you are experiencing has been added to the Master branch, is to just pull down that fix, then merge that into the stable version of the Engine that you are using to see if the fix corrects the issue for you.
Using the Master branch for project development may not be ideal. However, if you want to be able to experiment with fixes, updates, and new features before they go live, that is where you would want to go.