I think I've founded the issue.

My timmings are correct and in accordance with the datasheet.

However, I've seen that CS1 and CS2 were very sensitive to perturbations and in case of noise the display was altered even on the disabled side.
As I've wrapped the board, It may possible that there is HF noise. I've tried to add a ceramique capacitor and it sounds better.
I'll correct the wiring of the LCD (by using wires shorter....)

Well, I've to investigate more....


Thanks for your answer

Regards
Stephane