Hi there!
I am working with CombinedChartView at the moment and got some issue when marked attached

I've cloned current master repo (latest commit f48fbfc ) and edit CombinedChartViewController.m at ChartsDemo to make this issue reproducible. Please, edit setChartData like below:

- (void)setChartData
{
CombinedChartData *data = [[CombinedChartData alloc] initWithXVals:months];
data.lineData = [self generateLineData];
data.barData = [self generateBarData];
data.bubbleData = [self generateBubbleData];
//data.scatterData = [self generateScatterData];
//data.candleData = [self generateCandleData];
_chartView.data = data;
_chartView.marker = [[ChartMarker alloc] init];
[_chartView highlightValueWithXIndex:(ITEM_COUNT - 1) dataSetIndex:0 callDelegate:NO];
}

Here is stack trace from XCode:

Thread 1Queue : com.apple.main-thread (serial)
#0 0x00000001050c41a8 in specialized fatalErrorMessage(StaticString, StaticString, StaticString, UInt) -> () ()
#1 0x0000000104f71962 in ArrayBuffer.checkInoutAndNativeTypeCheckedBounds(Int, wasNativeTypeChecked : Bool) -> () ()
#2 0x0000000104f8b047 in Array.subscript.getter ()
#3 0x000000010205537f in CombinedChartData.getEntryForHighlight(ChartHighlight) -> ChartDataEntry? at /Users/alpari_dev/Downloads/charts_master/Charts/Charts/Classes/Data/Implementations/Standard/CombinedChartData.swift:223
#4 0x000000010211b6d6 in ChartViewBase.drawMarkers(context : CGContext) -> () at /Users/alpari_dev/Downloads/charts_master/Charts/Charts/Classes/Charts/ChartViewBase.swift:548
#5 0x0000000102143876 in BarLineChartViewBase.drawRect(CGRect) -> () at /Users/alpari_dev/Downloads/charts_master/Charts/Charts/Classes/Charts/BarLineChartViewBase.swift:277
#6 0x00000001021439c5 in @objc BarLineChartViewBase.drawRect(CGRect) -> () ()
#7 0x0000000103a9d3e5 in -UIView(CALayerDelegate) drawLayer:inContext:
#8 0x00000001069647ea in -CALayer drawInContext:
#9 0x0000000106853faa in CABackingStoreUpdate ()
#10 0x00000001069644d4 in **ZN2CA5Layer8display_Ev_block_invoke ()
#11 0x000000010696434a in CA::Layer::display() ()
#12 0x0000000106958e87 in CA::Layer::display_if_needed(CA::Transaction) ()
#13 0x0000000106958f17 in CA::Layer::layout_and_display_if_needed(CA::Transaction) ()
#14 0x000000010694d3c9 in CA::Context::commit_transaction(CA::Transaction*) ()
#15 0x000000010697b086 in CA::Transaction::commit() ()
#16 0x0000000103a0f19b in _afterCACommitHandler ()
#17 0x0000000102e87c37 in __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION** ()
#18 0x0000000102e87ba7 in __CFRunLoopDoObservers ()
#19 0x0000000102e7d7fb in __CFRunLoopRun ()
#20 0x0000000102e7d0f8 in CFRunLoopRunSpecific ()
#21 0x00000001070dbad2 in GSEventRunModal ()
#22 0x00000001039e2f09 in UIApplicationMain ()
#23 0x0000000101ac5f2f in main at /Users/alpari_dev/Downloads/charts_master/Charts/ChartsDemo/Supporting Files/main.m:20
#24 0x000000010638492d in start ()