Is it a cassette or manual loading machine ?
If the variation is across the plate travel direction through the ctp you should pay attention to the so-called primary positioning unit - the three solenoid activated push fingers aligning the plate.
Clean the exposure table carefully using detergent then alcohol, avoiding debris and fluids going down the vacuum holes. The table surface is milled and aluminium dust and residue will build up over time, hence plates slipping.
Put a 1.5 - 2 mm drill rotated gently by hand into these holes not more than 2 centimeters deep to make sure they're not clogged. I assume the vacuum pump does its job properly.
