When I open *.xt files from Dolphin on my KDE Plasma desktop Dolphin would lock up while kcachegrind ran and then when I exited kcachegrind Dolphin would complain:
KDEInit could not launch '/usr/bin/kcachegrind'
So what I’ve done is to create a custom kcachegrind.sh script to run xcachegrind properly and then re-associated *.xt files (application/x-kcachegrind) with the new script in Dolphin.
Bug fixed!