It's a (lib)samplerate related issue: both audio files are in 44k1 and your jackd is running at 48k nominal, so that playback (and export) takes the extra step in making the rate conversion on-the-fly. Somehow, there's still an damn bad old bug in there, in qtractor, that deserves to be tamed.
Please confirm that all is fine when you start jackd with -r44100.
One other thing: whenever qtractor segfaults while in export, it will leave jackd running in freewheel mode, which besides making qjackctl show a cryptic 1e+02% (=100%) DSP load figure, it is pretty useless and brain dead for all else and normal things. Restart jackd and that's it.
Ok, I've bite the bullet.
It's a (lib)samplerate related issue: both audio files are in 44k1 and your jackd is running at 48k nominal, so that playback (and export) takes the extra step in making the rate conversion on-the-fly. Somehow, there's still an damn bad old bug in there, in qtractor, that deserves to be tamed.
Please confirm that all is fine when you start jackd with -r44100.
One other thing: whenever qtractor segfaults while in export, it will leave jackd running in freewheel mode, which besides making qjackctl show a cryptic 1e+02% (=100%) DSP load figure, it is pretty useless and brain dead for all else and normal things. Restart jackd and that's it.
Cheers.