I coat my bed with a drop of ELMER'S glue mixed with water and gently wiped with a tissue. I have found then 1st layer problem: nozzle is touching the glass, and that lead to blocking filament, my TITAN growls and the gear gets quickly full of PLA powder.... Remedy: make sure your bed center is mirror clean, the sensor is troubled by PLA reflectivity and sees probably the bed more distant than it is really, thus fooling the controller. I loose 0,7mm, which make a 1st layer of .2 stuck to the glass.
I had exactly the same problem. That's why I fitted one of these and moved the IR sensor off the print-head.
