Looks like code:
const invertedY = rttSizeH - y - 1;
this._preparePickingBuffer(this._engine!, rttSizeW, rttSizeH, x, invertedY);
return await this._executePicking(x, invertedY, disposeWhenDone);
must be
const invertedY = rttSizeH - adjustedY - 1;
this._preparePickingBuffer(this._engine!, rttSizeW, rttSizeH, adjustedX, invertedY);
return await this._executePicking(adjustedX, invertedY, disposeWhenDone);