Is there a relationship between keyboard and display manager?

I have a keyboard problem (= random erratic behavior) that does not appear in the following logs: kernel logs (dmesg), /var/log/journal (journalctl) or /var/log/Xorg.0.log [less Xorg.0.log | grep -i keyboard]. The last time the problem occurred, instead of rebooting, I opened a tty2 console as root and restarted lightdm, the display manager. When the display was restored, the keyboard was no longer erratic: it behaved completely normally. Is there anything to learn from this strange behavior?

Question by mazda on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.