Exporting a working sf2 soundfont to sfz does not work in my case.
Here is a region definition in the Polyphone interface

The exported sfz file had
<region> sample=samples\sin_069_04400.wav
lokey=70 hikey=68
loop_start=15435
pitch_keycenter=69
but it should have
<region> sample=samples\sin_069_04400.wav
lokey=68 hikey=70
loop_start=15435
pitch_keycenter=69
Correcting this manually in the sfz file made things work.
Furthermore,
<region> sample=samples\q_saw_069_04400.wav
lokey=68 hikey=70
loop_end=9878
loop_start=13982
pitch_keycenter=69
loop_start and loop_and have wrong values which need to be exchanged like in
<region> sample=samples\q_saw_069_04400.wav
lokey=68 hikey=70
loop_start=9878
loop_end=13982
pitch_keycenter=69
Finally, the wav files contained in the samples folder are different from the original wav fils used to create the sf2 soundfont.