Most of the circles I do on lightburn turn out deformed in the lower left part, why could this be?

(note the image is rotated but I can assure you both of the circles are deformed in the lower left part)

Majority of these problems are mechanical in nature. Looseness, binding etc.

What kind of laser are you running? The previous recommendation pointing you down the mechanical issues path is the right path forward. More information on the make and model of your machine will help pinpoint recommended first fixes—there’s some backlash & wiggle room on one or two of the axes. Make sure each axis has tight but smooth movement.