Indeed, a bug report already existed for the bug affecting NVIDIA card (https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers/+bug/973096) and as explained in my first message, I am not using NVIDIA card (as well as many other users affected by this problem). This is why I opened this new bug report.
Thanks Erwan for the reply.
Indeed, a bug report already existed for the bug affecting NVIDIA card (https:/ /bugs.launchpad .net/ubuntu/ +source/ nvidia- graphics- drivers/ +bug/973096) and as explained in my first message, I am not using NVIDIA card (as well as many other users affected by this problem). This is why I opened this new bug report.