Swift crash initialising a property - objective-c

Question

I have a project in which I am using both objective-c and swift, not sure if this is relevant but might be.
I have a class defined as follows:
#objc public class BHCloudFileManager {
...
}
This class is a singleton and so has a property:
public class var sharedManager: BHCloudFileManager {
struct Singleton {
static let instance = BHCloudFileManager()
}
return Singleton.instance
}
And also declares an instance variable as such:
var cloudFilesAwaitingUpload: [BHCloudFile] = [] // crash happens on this line
It might be worth mentioning that BHCloudFile is an objective-c class whereas BHCloudFileManager is clearly a swift class. The sharedManager method is first called on launch from objective-c code.
Prior to my updating my Mac to Yosemite (there may have also been an Xcode upgrade but I'm not sure) this code all worked fine, but now I get a crash on the property initialisation line. My init() method appends to this array, but that shouldn't be an issue, should it?
If you have any idea what might be causing this it would be greatly appreciated, I'm at a bit of a loose end!
Platform:
Occurs on iOS 7.1 on an iPad 3rd gen. Does not occur on iOS 8.1 in the simulator.
Exception:
Thread 1: EXC_BREAKPOINT (code=EXC_ARM_BREAKPOINT, subcode=0xe7ffdefe)
Stack trace:
0 0x2bec10c4 in dyld_fatal_error ()
1 0x2bec1f06 in dyld::halt(char const*) ()
2 0x2bec369e in dyld::fastBindLazySymbol(ImageLoader**, unsigned long) ()
3 0x3b0e40d0 in dyld_stub_binder ()
4 0x0005346c in Sparkjar.BHCloudFileManager.init (Sparkjar.BHCloudFileManager.Type)() -> Sparkjar.BHCloudFileManager at /Users/georgegreen/Code/BeeHive/BeeHive/BeeHive/models/BHCloudFileManager.swift:22
5 0x00053328 in Sparkjar.BHCloudFileManager.__allocating_init (Sparkjar.BHCloudFileManager.Type)() -> Sparkjar.BHCloudFileManager ()
6 0x000532e8 in globalinit_func1 at /Users/georgegreen/Code/BeeHive/BeeHive/BeeHive/models/BHCloudFileManager.swift:30
7 0x0185902a in __swift_once_block_invoke ()
8 0x3b0bf81e in _dispatch_client_callout ()
9 0x3b0c760e in dispatch_once_f$VARIANT$mp ()
10 0x01859016 in swift_once ()
11 0x0005d4c0 in Sparkjar.BHCloudFileManager.(sharedManager.getter : Sparkjar.BHCloudFileManager).(Singleton #1).instance.mutableAddressor : Sparkjar.BHCloudFileManager at /Users/georgegreen/Code/BeeHive/BeeHive/BeeHive/models/BHCloudFileManager.swift:30
12 0x000532b8 in Sparkjar.BHCloudFileManager.sharedManager.getter : Sparkjar.BHCloudFileManager at /Users/georgegreen/Code/BeeHive/BeeHive/BeeHive/models/BHCloudFileManager.swift:32
13 0x000533b0 in #objc Sparkjar.BHCloudFileManager.sharedManager.getter : Sparkjar.BHCloudFileManager ()
14 0x00170570 in -[BHAppDelegate setupApplication] at /Users/georgegreen/Code/BeeHive/BeeHive/BeeHive/BHAppDelegate.m:54
15 0x00170414 in -[BHAppDelegate application:didFinishLaunchingWithOptions:] at /Users/georgegreen/Code/BeeHive/BeeHive/BeeHive/BHAppDelegate.m:41
16 0x327b95a6 in -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] ()
17 0x327b8efa in -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] ()
18 0x327b358a in -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] ()
19 0x3274f708 in -[UIApplication handleEvent:withNewEvent:] ()
20 0x3274e870 in -[UIApplication sendEvent:] ()
21 0x327b2cc8 in _UIApplicationHandleEvent ()
22 0x34d95aec in _PurpleEventCallback ()
23 0x34d956d6 in PurpleEventCallback ()
24 0x2fef8ab6 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ ()
25 0x2fef8a52 in __CFRunLoopDoSource1 ()
26 0x2fef7226 in __CFRunLoopRun ()
27 0x2fe61f4e in CFRunLoopRunSpecific ()
28 0x2fe61d32 in CFRunLoopRunInMode ()
29 0x327b1ef0 in -[UIApplication _run] ()
30 0x327ad16c in UIApplicationMain ()
31 0x001ab948 in main at /Users/georgegreen/Code/BeeHive/BeeHive/BeeHive/main.m:16