It seems dispcal is hanging before it gets to writing out the .cal file. If you open up a system monitor, you should see a zombie dispcal process. End it, and you should find any files in ~/.local/share/dispcalGUI/storage/incomplete. In case a .cal file was generated, you can drag & drop it into dispcalGUI main window to continue where you left off (deactivate “Interactive display adjustment” and set tone curve to “As measured” on the “Calibration” tab to use the existing cal file as a base for profiling).
I’d also recommend updating to Argyll CMS 1.8, 1.5.1 is very old now.