Okay...
i re-recorded my instruments in (min) 44100 kHz. redone the monolith and all is fine.
NOTE: i first create an .sfz encapsulation in ESC, just because i feel it more fun to import my samples inside HISE than direct .wav (.sfz has root note, start end sample, start end loop, etc. .. that is automaticly set up in HISE when importing)
when creating monolith a line is added in the samplemap.xml:
"MonolithOffset="value" MonolithLength="value" SampleRate="44100"/>"
maybe something wrong beetween the 27.8 kHz data infos inside the wav, the .sfz info and this line created in the samplemap file ?
BTW, with brand new 44100 kHZ or above samplerate: all is good ;)