An even better fix was found in the Klipper discord by xF4m3 and XeroX:
In case you still have this issue after updating today, i found this fix in the voron discord klipper channel (its a pinned message there)
EDIT: Latest Debian 11 changed by intention or accident by-id and by-path mapping in systemd. This fixes the issue when klipper is not able to connect after recent update of Apr 29th 2023.
Make sure you’re root or using sudo -s before. Reboot is mandatory.
sed -i ‘/^SUBSYSTEMS==“pci”, ENV{ID_BUS}=“pci”./i SUBSYSTEMS==“usb”, IMPORT{builtin}=“usb_id”, IMPORT{builtin}=“hwdb --subsystem=usb”’ /lib/udev/rules.d/60-serial.rules
sed -i 's/^SUBSYSTEMS==“pci”, ENV{ID_BUS}=“pci”./SUBSYSTEMS==“pci”, ENV{ID_BUS}==“”, ENV{ID_BUS}=“pci”, \
ENV{ID_VENDOR_ID}=“$attr{vendor}”, ENV{ID_MODEL_ID}=“$attr{device}”, \
IMPORT{builtin}=“hwdb --subsystem=pci”/g’ /lib/udev/rules.d/60-serial.rules
sed -i ‘/ENV{MODALIAS}==".*/d’ /lib/udev/rules.d/60-serial.rules
The initial workaround was changing to by-path, but this does not work if you change ports. This workaround should fix it permanently and does not collide with future updates of debian.