kubuntu – Frozen app? Stuck spinner/Dolphin icon on the task bar

Kubuntu 21.04, Plasma 5.21.4

I’ve got a blinking Dolphin icon on my task bar. It looks like it’s starting-dying-starting-dying, however KSysGuard System Monitor doesn’t show anything. I can open Dolphin, really open it – and it gets its own icon on the task bar and works fine. If I use the “Kill A Window” option, it kills the task bar as well. How do I identity the process causing it, and shut it down?