Obviously, I did not precise that it happened after adding a firewire card on the PCIE-1 slot. I also did a system upgrade at the same time. After removing the firewire extension card, well, the problem persisted. I notice that this box would resume normally if it is suspended in a virtual terminal. And I recalled I had a similar problem on my laptop. I dropped this script in /usr/lib/systemd/system-sleep/ : #!/bin/bash if [ "$1" = "pre" ];then chvt 2 fi if [ "$1" = "post" ];then chvt 1 fi exit 0 The machine would then resume in KDE, after switching to a virtual terminal with no $DISPLAY on suspend, and back to VT 1 on resume. It does so with the firewire extension card back in place also. This seems to be related to KDE, and not the presence of a firewire card in the box. Sorry to have bothered you. Happy New Year !