Not sure how it works, but I accidentally clicked "+" on LoopEnd and that fixed the problem! Looks like Sampler counts sample length differently or something.
My loop end point is exactly at the end of the sample so I shouldn't be able to increase LoopEnd position by clicking "+", but all samples have +1 "gap" at the end of the sample.
And if the loop region is in the middle of the sample, then "+1" or "-1" on LoopEnd or LoopStart fixes the problem.
Maybe this will be useful for someone :)
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@DabDab I'm using MIDI scripts like these
@hisefilo You can't transpose by cents (a keyboard doesn't have cents) what you want is to change tune. Use Message.setFineDetune(). And for transposing you ...
Forum (forum.hise.audio)
@Lindon Slight tweak that shows you the current setting for the inbound note: HiseSnippet 1383.3oc4XstaSbDEd13rQXSMpTgZqTUkFE0eXDTiMkakTDFxETTIDq3.sRHDcxtGGO...
Forum (forum.hise.audio)
And there is built-in Transpose MIDI script in HISE
@Christoph-Hart ahhh, thanks! 8 should be enough.
@d-healey Well, that was easy. Thanks a lot for your help! This is my first experience with development.
For some reason it only compiled VST, but at least it works :)
@d-healey Thanks! I'm going to watch all your videos some day, they're very helpful!
@lalalandsynth You can't modulate sample start with Wavetable. So if you want to use unison + detune (like in a regular synth) to make some typical synth lead it will sound kinda weird, with some flanger effect.
@d-healey Thanks again, will try this option for now. But hopefully Christoph will fix this in some future updates.
@d-healey unfortunately, Hise still crashes when I turn octave or semi tone knobs.
@Lindon I tried to add per-filtering before and after, it still crashes.
@d-healey oh, so it's not just me :) Thank you for taking time to figure out this issue.
I don't think the user will go that low, but it possible that someone accidentally find this bug (like I did) and will be annoyed by ruined session.
@d-healey it's on top, after the Interface script. And Transposer is on Sampler level.
BTW I switched to MBP and the issue is still there. Midi keyboard is the same.
@d-healey Well, when I set to -5 then only C-2 crashes Hise, C#-2 and above - all good.
But when I set -6, then it starts crashing on C-2 and C#-2
aaaaand if it's -7, then it starts crashing from D-2. Like there is some dependency 
@d-healey If you mean to test it with the mouse then yes, it crashes Hise.
@d-healey I rarely use it and I don't know how to switch octaves, it's always plays higher ranges.
Here is the project. NoteRangeTest.zip
@d-healey Will do that in few minutes. If I do it with the mouse like you, then it works fine, but when I press the lowest key on the midi keyboard it crashes.