It turns out that the problem is an incompatibility with the packages
network-manager + network-manage-gnome
Whenever these are installed, usbserial becomes intransparent
(i.e., physical and logical devices are present, but there is no thoughput through the serial interface).
After removal of these packages and after system restart the serial interface works as it should.
Maybe this should be considered a bug of one of these packages.
It turns out that the problem is an incompatibility with the packages
network-manager + network- manage- gnome
Whenever these are installed, usbserial becomes intransparent
(i.e., physical and logical devices are present, but there is no thoughput through the serial interface).
After removal of these packages and after system restart the serial interface works as it should.
Maybe this should be considered a bug of one of these packages.