Your saw blade needs to be aligned with the arbor of the motor. This is impossible if the collars are not clean and in good shape. Any high spot on the arbor will distort the saw blade. It may distort the blade so the blade stays flat but is no longer truly perpendicular to the collar or it may distort the blade so that it is no longer perfectly flat. Also see our article on Cleaning Saw Blades.
Remember, please, that a saw blade is tensioned and is, in effect, a flat spring.
It is not unusual to examine a saw blade and see debris embedded in the saw plate. Also common is to find two rings on the saw plate where the edges of the collars contacted the plate but the center of the collars did not.
Every time a saw blade is changed the collars, even if they are just a flanged nut, should be examined for cleanliness and flatness.