@axt.: Yes, the kernels are properly installed, I reinstalled them without error before reporting. I understand that 4.15 is old, but I supposed that there is the same issue on Ubuntu Xenial (you are right, I should have test it, and I will try to do it).
@kaihengfeng: I could not find 4.15.0-56 and 4.15.0-57: could you tell me where I can get them?
@axt.: Yes, the kernels are properly installed, I reinstalled them without error before reporting. I understand that 4.15 is old, but I supposed that there is the same issue on Ubuntu Xenial (you are right, I should have test it, and I will try to do it).
@kaihengfeng: I could not find 4.15.0-56 and 4.15.0-57: could you tell me where I can get them?