Glad I found this thread...
I bought a Lenovo Yoga 9i Gen 7, it comes with the Precision Pen 2... Since the very first moment I put a screen protector, and when tried the pen for the first time I realized that when drawing diagonals lines they were all "wavy" (as the red lines in the screenshot attached), the weird thing is that only for diagonals, the "straight" ones are drawn well, the same happened to you? I wanna believe it's the screen protector and not a faulty screen or pen... I should remove the screen protector to test but I had a hard time getting one for this model here in Spain haha.