Drawing problem with Ubook X

Good morning to Everyone.
I have a problem of efficiency with my Ubook X, detected during the drawing works and with all the different application for digital drawing installed on the tablet (Paint, OneNote, Photoshop and Sketchbook).
The problem: when I draw diagonal lines the digital signs producted by the pen on the screen (I purchased both the HiPen H6 as the HiPen H7) are distorted and corrugated despite my hand movement is accurate, linear and fluid. But, if I draw lines in orizzontal or vertical direction, the tablet instead produce the right effect of the digital lines. Seeking to solve the problem, I tried to do the calibration procedure of the screen in WIN 10 and at the same time the calibration of the Bluetooth devices HiPens. This work didn’t give me any result and the problem there is again.
Have you solution? Thanks. Marco