HUGE GRAPHIC GLITCHES in arrangement window

Hi everyone,

Is anyone experiencing those graphic glitches that appear on tracks , no matter the type ?
The screenshots in this post to illustrate the following problem :
I’ve recorded something on an instrument track , and found nothing in the region … but when I open the piano roll editor, the notes are here !
Then I’ve made a render in place of the instrument track and … same thing : nothing in the audio region of the arrangement window, but when I open the audio editor, the waveform is there !

The problem is that I can’t edit anything in the arrangement window !
Please could someone advise me on this ? It never happened with the previous versions of Cubase I owned (7 and 7.5)
Thanks !