Thread 1: EXEC_BAD_ACCESS (code=1), address=0x6000000000000018) - sprite-kit

Question

Read all of the posts regarding this error being memory related and trying to access something that is no longer there.
Problem: Error pops up at virtually random intervals. It can appear after the first enemy is killed or the Nth enemy is killed. However, it ONLY appears when an enemy is killed.
Testing: Running iOS 8 beta 5, Xcode 6 beta 5 on iPhone 5s.
Code flow:
Enemy SKNodes class instances are created at start of level and stored in NSMutableArray for reference:
Goblin *newGoblin = [[Goblin alloc] initFacingDirection:1];
// set various properties…
[enemyGoblins addObject:newGoblin];
Player’s sword makes contact with enemy:
NSMutableArray *discardedItems = [NSMutableArray array];
for(Goblin *object in enemyGoblins)
{
[object runBloodBurst:true damagePoints:_player.swordDamage];
if(object.goblinHealth < 0)
[discardedItems addObject:object];
}
if([discardedItems count] > 0)
[enemyGoblins removeObjectsInArray:discardedItems];
In the Goblin class, the “die” code is:
if(self.goblinHealth < 0)
{
SKAction *wait0 = [SKAction waitForDuration:1.0];
SKAction *block0 = [SKAction runBlock:^{
[self removeActionForKey:#"animation"];
[self runAction:[_animations goblin_dieLeft]];
}];
SKAction *block1 = [SKAction runBlock:^{
[self removeFromParent];
}];
[self runAction:[SKAction sequence:#[block0, wait0, block1]]];
}
What I’ve tried:
I disabled the “discardedItems” code because I thought ARC might dump the object from memory once the reference was lost and the subsequent Goblin class’ “die animation” would cause the crash but this did not resolve the issue.
I tried zombies and breakpoints but got no useful clues either.
Am I barking up the wrong tree in regards to what I’ve tried or has anyone experienced a similar issue in Beta 5?
EDIT
Here is the backtrace:
(lldb) bt
* thread #1: tid = 0x3264b, 0x000000018cb13434 SpriteKitSKCSprite::update(double) + 404, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x7000000000000018)
frame #0: 0x000000018cb13434 SpriteKitSKCSprite::update(double) + 404
frame #1: 0x000000018cb13440 SpriteKitSKCSprite::update(double) + 416
frame #2: 0x000000018cb13440 SpriteKitSKCSprite::update(double) + 416
frame #3: 0x000000018cacbf28 SpriteKit-[SKScene _update:] + 140
frame #4: 0x000000018cae63f8 SpriteKit-[SKView(Private) _update:] + 568
frame #5: 0x000000018cae3a10 SpriteKit-[SKView renderCallback:] + 764
frame #6: 0x000000018cae0a9c SpriteKit__29-[SKView setUpRenderCallback]_block_invoke + 60
frame #7: 0x000000018cb0d890 SpriteKit-[SKDisplayLink _callbackForNextFrame:] + 272
frame #8: 0x000000010042ca9c libglInterpose.dylib-[DYDisplayLinkInterposer forwardDisplayLinkCallback:] + 168
frame #9: 0x000000018c615b90 QuartzCoreCA::Display::DisplayLinkItem::dispatch() + 32
frame #10: 0x000000018c615a28 QuartzCoreCA::Display::DisplayLink::dispatch_items(unsigned long long, unsigned long long, unsigned long long) + 324
frame #11: 0x00000001897dddc0 IOKitIODispatchCalloutFromCFMessage + 376
frame #12: 0x00000001885dcf34 CoreFoundation__CFMachPortPerform + 180
frame #13: 0x00000001885f1b38 CoreFoundation__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 56
frame #14: 0x00000001885f1a98 CoreFoundation__CFRunLoopDoSource1 + 436
frame #15: 0x00000001885efa18 CoreFoundation__CFRunLoopRun + 1640
frame #16: 0x000000018851d664 CoreFoundationCFRunLoopRunSpecific + 396
frame #17: 0x000000019154f5a4 GraphicsServicesGSEventRunModal + 168
frame #18: 0x000000018ccd6164 UIKitUIApplicationMain + 1488
* frame #19: 0x0000000100165530 CarcerQuestmain(argc=1, argv=0x000000016fdab9d8) + 116 at main.m:16
frame #20: 0x000000019885aa08 libdyld.dylibstart + 4
(lldb)

Answer 1

change
[self runAction:[SKAction sequence:#[block0, wait0, block1]]];
to
[self runAction:[SKAction sequence:#[block0, wait0]] completion:^{
[_self removeFromParent];
}];
I ran in to the same issue when updating IOS7 code to run on IOS8, and using the completion block fixed the issue.

Answer 2

Reading through the comments of your question, I'm not sure if you've solved this problem, and your code snippet isn't complete enough for me to see your issue, but I recently ran into a similar problem and it took me a while to figure out, so I'd post it in case it's helpful to you or some future reader of the post.
You can see my code change here: https://github.com/ik/2048/commit/3ffec547367320c7e179624a14ac5867ed1acea2
Basically what happens is runAction is async. It is executed in the next screen refresh cycle (hence the display link call in your stack trace). So if you call removeSomething after your runAction, it can be executed before the action is run, and you will crash.
At least that's what caught me - I don't know why it never occurred in iOS 7. See code below.
- [self removeFromParentCell]; // Used to call it here - wrong.
SKAction *wait = [SKAction waitForDuration:GSTATE.animationDuration];
SKAction *remove = [SKAction removeFromParent];
- [self runAction:[SKAction sequence:#[wait, remove]]];
+ [self runAction:[SKAction sequence:#[wait, remove]] completion:^{
+ [self removeFromParentCell]; // This is right.
+ }];

Answer 3

After scouring the Apple Support Forums and running the same project on iOS 7, it appears this is a Beta release bug and not faulty code after all.