probably a known problem related to JACK's alsa_in/alsa_out adapters, aka. "ALSA Bridge" on KXStudio's JACK frontend (Cadence), conflicting with jackd-freewheel run mode.
if it's the case, turn off or stop the so called alsa-bridge (from cadence) and try again; hopefully it won't freeze anymore on qtractor (or ardour) export procedure.
probably a known problem related to JACK's alsa_in/alsa_out adapters, aka. "ALSA Bridge" on KXStudio's JACK frontend (Cadence), conflicting with jackd-freewheel run mode.
if it's the case, turn off or stop the so called alsa-bridge (from cadence) and try again; hopefully it won't freeze anymore on qtractor (or ardour) export procedure.
hth.
cheers