Problems with Yoshimi

Hi, gang!!!
I use MuseScore 3.6.2 inside Ubuntu Studio 22.04.1 LTS (64 bit Linux).
Also, I use Jack Audio Connection Kit to "cable" between audio and MIDI devices and apps.
So, I tried to use MuseScore with Yoshimi (Linux synthesizer) and I have a very weird issue:
Whatever the score I use, the first note (first beat of the first bar) of the song (whatever the rythm and/or pitch) aren't played.
The sound starts with the second beat notes.
What I'm doing wrong? What did I forget?
Also, it isn't a "problem" indeed, but...
How could we have an instrument definition according with the Yoshimi sound banks?
It isn't a General MIDI configuration.
Some idea?
Blessings and Greetings from Chile!!!