I think, I found Bugs in Dukascopy's Historical Data(between 1st October 2004 and 25th October 2004).
e.g.
Historical Data of Period.ONE_HOUR was broken.
Please check this strategy.

package jforex;

import com.dukascopy.api.*;
import java.text.SimpleDateFormat;
import java.util.TimeZone;
import java.util.Locale;
import java.util.Calendar;
import java.util.List;
import java.util.ArrayList;
import java.util.Arrays;

public class getBarsCheck implements IStrategy {
    
    private static Calendar myCalendarFrom;
    private static Calendar myCalendarTo;
    static {
        myCalendarFrom = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
        myCalendarFrom.set(2004, Calendar.OCTOBER, 1, 0, 0, 0);
        myCalendarFrom.set(Calendar.MILLISECOND, 0);
        myCalendarTo = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
        myCalendarTo.set(2004, Calendar.OCTOBER, 25, 0, 0, 0);
        myCalendarTo.set(Calendar.MILLISECOND, 0);
    }
    @Configurable(value="Check Time: From", obligatory=true, description="1st October 00:00 (include this time)")
    public Calendar calFrom = myCalendarFrom;
    @Configurable(value="Check Time: To", obligatory=true, description="25th October 00:00 (not include this time)")
    public Calendar calTo = myCalendarTo;
    @Configurable(value="Check Instrument", obligatory=true)
    public Instrument instrument = Instrument.EURUSD;
    @Configurable(value="Check Period", obligatory=true)
    public List<Period> checkPeriods = new ArrayList<Period>(Arrays.asList(new Period[]{Period.DAILY, Period.FOUR_HOURS, Period.ONE_HOUR, Period.FIFTEEN_MINS, Period.FIVE_MINS}));
    
    public void onStart(IContext context) throws JFException {
        IHistory history = context.getHistory();
        IConsole console = context.getConsole();
        console.getOut().println("getBarsCheck: Started");
        
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss",Locale.US);
        sdf.setTimeZone(TimeZone.getTimeZone("GMT"));
        
        long timeFrom = calFrom.getTimeInMillis(), timeTo;
        console.getOut().println("from: "+sdf.format(timeFrom));
        console.getOut().println("to: "+sdf.format(calTo.getTimeInMillis()));
        for(Period period: checkPeriods){
            timeTo = history.getPreviousBarStart(period, calTo.getTimeInMillis());
            List<IBar> barList = history.getBars(instrument, period, OfferSide.BID, timeFrom, timeTo);
            double volumeSum = 0;
            for(IBar bar: barList){volumeSum += bar.getVolume();}
            console.getOut().println("[" + period + "]" + " List Size = " +barList.size() + ", Volume Total = " + volumeSum);
        }
        console.getOut().println("getBarsCheck: Done");
        context.stop();
    }

    public void onAccount(IAccount account) throws JFException {}
    public void onMessage(IMessage message) throws JFException {}
    public void onStop() throws JFException {}
    public void onTick(Instrument instrument, ITick tick) throws JFException {}
    public void onBar(Instrument instrument, Period period, IBar askBar, IBar bidBar) throws JFException {}
}

Result is this.


And also, Historical Data of Period.FIVE_MINS(between 19th October 2004 and 25th October 2004) was broken.

List size = 0!
What is this!!

Regards.

And There is something Bug in IHistory.getBars(Instrument instrument, Period period, OfferSide side, Filter filter, int numberOfCandlesBefore, long time, int numberOfCandlesAfter).

e.g.

package jforex;

import com.dukascopy.api.*;
import java.text.SimpleDateFormat;
import java.util.TimeZone;
import java.util.Locale;
import java.util.Calendar;
import java.util.List;
import java.util.ArrayList;
import java.util.Arrays;

public class getBarsCheck2 implements IStrategy {
    
    private static Calendar myCalendarFrom;
    private static Calendar myCalendarTo;
    static {
        myCalendarFrom = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
        myCalendarFrom.set(2004, Calendar.NOVEMBER, 19, 21, 55, 0);
        myCalendarFrom.set(Calendar.MILLISECOND, 0);
        myCalendarTo = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
        myCalendarTo.set(2004, Calendar.NOVEMBER, 19, 22, 00, 0);
        myCalendarTo.set(Calendar.MILLISECOND, 0);
    }
    @Configurable(value="Check Time: From", obligatory=true, description="15th Octber 22:00 (include this time)")
    public Calendar calFrom = myCalendarFrom;
    @Configurable(value="Check Time: To", obligatory=true, description="15th Octber 23:00 (not include this time)")
    public Calendar calTo = myCalendarTo;
    @Configurable(value="Check Instrument", obligatory=true)
    public Instrument instrument = Instrument.EURUSD;
    @Configurable(value="Check Period", obligatory=true)
    public Period checkPeriod = Period.FIVE_MINS;
    
    public void onStart(IContext context) throws JFException {
        IHistory history = context.getHistory();
        IConsole console = context.getConsole();
        console.getOut().println("getBarsCheck2: Started");
        
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss",Locale.US);
        sdf.setTimeZone(TimeZone.getTimeZone("GMT"));
        
        long timeFrom = calFrom.getTimeInMillis(), timeTo;
        console.getOut().println("from: "+sdf.format(timeFrom));
        console.getOut().println("to: "+sdf.format(calTo.getTimeInMillis()));
        timeTo = history.getPreviousBarStart(checkPeriod, calTo.getTimeInMillis());
        List<IBar> askBars = history.getBars(instrument, checkPeriod, OfferSide.ASK, Filter.NO_FILTER, timeFrom, timeTo);
        List<IBar> bidBars = history.getBars(instrument, checkPeriod, OfferSide.BID, Filter.NO_FILTER, timeFrom, timeTo);
        console.getOut().println("[" + checkPeriod + "]" + " AskBar Size = " +askBars.size() + ", BidBar Size = " + bidBars.size());
        askBars = history.getBars(instrument, checkPeriod, OfferSide.ASK, Filter.ALL_FLATS, 1, timeFrom, 1);
        bidBars = history.getBars(instrument, checkPeriod, OfferSide.BID, Filter.ALL_FLATS, 1, timeFrom, 1);
        console.getOut().println("[" + checkPeriod + "]" + " BidBar Size = " +askBars.size() + ", AskBar Size = " + bidBars.size());
        console.getOut().println("getBarsCheck2: Done");
        context.stop();
    }

    public void onAccount(IAccount account) throws JFException {}
    public void onMessage(IMessage message) throws JFException {}
    public void onStop() throws JFException {}
    public void onTick(Instrument instrument, ITick tick) throws JFException {}
    public void onBar(Instrument instrument, Period period, IBar askBar, IBar bidBar) throws JFException {}
}

P.S. At least before this weekend, this error didn't exist.
regards.