I have a lot of experience with the sfz format but not specifically with sforzando.
My experience is all players have quirks and some even crash on some commands.
I assume what you sent is only part of a larger file, because the group command only
makes sense if you have multiple regions. Also, what you sent will only sound
between note numbers 50-70. So possibly the same sound is being
called up multiple times in overlapping areas.
There is a lot of unnecessary stuff, too. I can imagine the round-robin sequencer
may be confusing sforzando. Reduce your file to the basics:
<group>
hikey=70
lokey=50
<region>
sample=..\..\..\Zoom Import\E4Loud.MP3
Also, consider putting your samples together with your sfz file and change the reference.
sample=E4Loud.MP3
This is just so if you decide to move your sound, everything will move together.
Otherwise you move the sfz file and it won't find the sound files anymore.