I have an older computer, bought around 2003, Core Duo 3.0 Ghz with 2 Gigs Ram. I'm running Linux Mint 18.2, with KDE, all patches up to date.
I've had this issue in the past, but don't recall doing anything other than rebooting and that resolved it. However, for the past few days it persists thru reboots and everything that I've tried. 90% of the time, one of these 2 scenarios occur. 1) I close Konsole and one of the CPU cores spikes to 100%. This persists till I kill the PID. Or 2) the next time I try to open Konsole it won't open. I see it for a moment in the Task Manager, but then it vanishes. This does not clear until I reboot.

Bump, running into this too after recent update. If I KILL all konsole processes, I cannot start it again unless I start it from some other process such as xterm. Konsole seems to work ok but if I close all konsole windows then one remaining konsole process spikes 100% utilization (of one CPU).