A quick visual overview of why a 3 point leveling system on a 3d printer is better than a 4 point system.
I didn't say in the video but if your glass plate, if you have one, will not be in perfect contact with the aluminium plate and not transferring its heat efficiently.
If you are not using glass then you could be suffering from bad adhesion problems that you just can't fix. One problem I was having when I moved to using a glass plate was the screws were pushing down upon the acrylic Y carriage and warping it because the glass doesn't bend and it ended up crashing into the frame so I had to replace the acrylic with an aluminium. Probably wouldn't have been a problem with 3 points of contact.