I think that’s possibly due to envelope retrigger mode which I think is located on the Trig page. Not sure if this is what it is but the envelope behaviour is legato by default I think and so doesn’t behave as you’d expect. In the past that had me scratching my head when I first got mine a few years ago. I suppose one way to determine if it’s that is to make the amp envelope release time zero.

Take this with a pinch of salt, I don’t use samples very often on mine so it could be something else.