No reproduction project but seems like it could be a regression of 707761.
Periodic crash on editor startup. seen on 5.3.4p3. The following callstack is produced

Initialize mono
Mono path[0] = '/Applications/Unity/Unity.app/Contents/Frameworks/Managed'
Mono path[1] = '/Applications/Unity/Unity.app/Contents/Frameworks/Mono/lib/mono/2.0'
Mono config path = '/Applications/Unity/Unity.app/Contents/Frameworks/Mono/etc'
Using monoOptions --debugger-agent=transport=dt_socket,embedding=1,defer=y,address=0.0.0.0:56546
2016-06-21 19:49:52.803 Unity[19546:622243] NSDocumentController Info.plist warning: The values of CFBundleTypeRole entries must be 'Editor', 'Viewer', 'None', or 'Shell'.
...300157 bytes written to /Users/pyamamoto/Library/Unity/Certificates/CACerts.pem

LICENSE SYSTEM [2016621 19:49:53] Next license update check is after 2015-07-03T22:33:36

IsTimeToCheckForNewEditor: Update time 1466555535 current 1466563796
/Users/pyamamoto/Documents/ws_git/ws_texas5/dev/poker-client/client-unified/zynga-casino
Rebuilding Library because the asset database could not be found!

(Filename: /Users/builduser/buildslave/unity/build/Editor/Src/AssetPipeline/AssetInterface.cpp Line: 2052)

EditorUpdateCheck: Response {latestversionstring: '5.3.5f1 (960ebf59018a)', latestversion: '99999', latestversionmessage: '', updateurl: 'http://unity3d.com/update/', updateinterval: '3600'} updateurl = http://unity3d.com/update/ interval = 3600
GetManagerFromContext: pointer to object of manager 'MonoManager' is NULL (table index 5)

(Filename: /Users/builduser/buildslave/unity/build/Runtime/BaseClasses/ManagerContext.cpp Line: 89)

Unity(19546,0x7fff73d24000) malloc: *** error for object 0x11c182d40: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
Stacktrace:

Native stacktrace:

0 libsystem_kernel.dylib 0x00007fff81cf4f06 __pthread_kill + 10
1 libsystem_c.dylib 0x00007fff948616e7 abort + 129
2 libsystem_malloc.dylib 0x00007fff81d04041 szone_size + 0
3 Chromium Embedded Framework 0x0000000106e38d88 catch_exception_raise + 1683464
4 Chromium Embedded Framework 0x0000000106e36895 catch_exception_raise + 1674005
5 Chromium Embedded Framework 0x0000000106ea15e6 catch_exception_raise + 2111590
6 Chromium Embedded Framework 0x0000000106ea8a59 catch_exception_raise + 2141401
7 libobjc.A.dylib 0x00007fff95eb2b3b _ZN12_GLOBAL__N_119AutoreleasePoolPage3popEPv + 477
8 CoreFoundation 0x00007fff943c0c12 _CFAutoreleasePoolPop + 50
9 Foundation 0x00007fff91cbc84a -[NSAutoreleasePool drain] + 153
10 Chromium Embedded Framework 0x00000001087af549 _CTFontManagerUnregisterFontForData + 24595817
11 Chromium Embedded Framework 0x00000001061e2706 cef_zip_reader_create + 132998
12 Chromium Embedded Framework 0x00000001061e27de cef_zip_reader_create + 133214
13 Chromium Embedded Framework 0x00000001061e1bd7 cef_zip_reader_create + 130135
14 libsystem_c.dylib 0x00007fff9486246b __cxa_finalize_ranges + 345
15 libsystem_c.dylib 0x00007fff9486276f exit + 55
16 Unity 0x0000000101c39ef3 _Z17LaunchBugReporter13BugReportMode + 35
17 Unity 0x0000000101a2eb67 _ZN17EditorMonoConsole26LogToConsoleImplementationERKSsiPKciiiiPFvRK11CppLogEntryE + 1191
18 Unity 0x0000000101a2f0fd _Z26LogToConsoleImplementationRKSsiPKciiiiPFvRK11CppLogEntryE + 173
19 Unity 0x00000001012b2c53 _Z40DebugStringToFilePostprocessedStacktracePKcS0_S0_iS0_iiiiPFvRK11CppLogEntryE + 1235
20 Unity 0x00000001012b1707 _Z17DebugStringToFilePKciS0_iiiiPFvRK11CppLogEntryE + 375
21 Unity 0x0000000100c31999 _Z21GetManagerFromContexti + 169
22 Unity 0x00000001011409be _Z20FindStaticMonoMethodPKcS0_ + 30
23 Unity 0x000000010115bc42 _Z20CallStaticMonoMethodPKcS0_PPvPP13MonoException + 34
24 Unity 0x000000010115bc19 _Z20CallStaticMonoMethodPKcS0_PPv + 25
25 Unity 0x000000010199b12c _ZN12_GLOBAL__N_118UpdateCheckMessage4DoneEv + 1292
26 Unity 0x00000001019814b6 _ZN11CurlRequest5CheckEv + 806
27 Unity 0x000000010197f960 _Z16CurlRequestCheckv + 80
28 Unity 0x0000000101c5d0c5 -[OSXNativeWebViewWindowHelper tickTimer] + 85
29 Foundation 0x00007fff91d4dd6c __NSFireTimer + 95
30 CoreFoundation 0x00007fff9440ab94 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20
31 CoreFoundation 0x00007fff9440a823 __CFRunLoopDoTimer + 1075
32 CoreFoundation 0x00007fff9440a37a __CFRunLoopDoTimers + 298
33 CoreFoundation 0x00007fff94401871 __CFRunLoopRun + 1841
34 CoreFoundation 0x00007fff94400ed8 CFRunLoopRunSpecific + 296
35 HIToolbox 0x00007fff84b94935 RunCurrentEventLoopInMode + 235
36 HIToolbox 0x00007fff84b9476f ReceiveNextEventCommon + 432
37 HIToolbox 0x00007fff84b945af _BlockUntilNextEventMatchingListInModeWithFilter + 71
38 AppKit 0x00007fff89c51efa _DPSNextEvent + 1067
39 AppKit 0x00007fff89c5132a -[NSApplication _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 454
40 AppKit 0x00007fff89ec0b4e -[NSApplication _doModalLoop:peek:] + 653
41 AppKit 0x00007fff8a0a179b __35-[NSApplication runModalForWindow:]_block_invoke + 126
42 AppKit 0x00007fff89ebe441 -[NSApplication runModalForWindow:] + 156
43 AppKit 0x00007fff8a04500b _NXDoLocalRunAlertPanel + 402
44 AppKit 0x00007fff8a097064 __NSRunInformationalAlertPanel_block_invoke + 44
45 AppKit 0x00007fff8a096ee7 NSRunInformationalAlertPanel + 425
46 Unity 0x0000000101c43e79 _Z13DisplayDialogRKSsS0_S0_S0_ + 425
47 Unity 0x000000010144d0e3 _ZN14AssetInterface10InitializeEbbPi + 12387
48 Unity 0x00000001019ea050 _ZN11Application17InitializeProjectEv + 6272
49 Unity 0x0000000101c3f256 -[EditorApplication applicationDidFinishLaunching:] + 518
50 CoreFoundation 0x00007fff94418bbc __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 12
51 CoreFoundation 0x00007fff94418b4f ___CFXRegistrationPost_block_invoke + 63
52 CoreFoundation 0x00007fff94418ac7 _CFXRegistrationPost + 407
53 CoreFoundation 0x00007fff94418832 ___CFXNotificationPost_block_invoke + 50
54 CoreFoundation 0x00007fff943d55e2 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1922
55 CoreFoundation 0x00007fff943d4835 _CFXNotificationPost + 693
56 Foundation 0x00007fff91caafda -[NSNotificationCenter postNotificationName:object:userInfo:] + 66
57 AppKit 0x00007fff89d9c459 -[NSApplication _postDidFinishNotification] + 297
58 AppKit 0x00007fff89d9c1c3 -[NSApplication _sendFinishLaunchingNotification] + 203
59 AppKit 0x00007fff89c56e9d -[NSApplication(NSAppleEventHandling) _handleAEOpenEvent:] + 557
60 AppKit 0x00007fff89c56947 -[NSApplication(NSAppleEventHandling) _handleCoreEvent:withReplyEvent:] + 250
61 Foundation 0x00007fff91cf962d -[NSAppleEventManager dispatchRawAppleEvent:withRawReply:handlerRefCon:] + 290
62 Foundation 0x00007fff91cf94a7 _NSAppleEventManagerGenericHandler + 102
63 AE 0x00007fff819e6261 _Z20aeDispatchAppleEventPK6AEDescPS_jPh + 531
64 AE 0x00007fff819e5fe8 _ZL25dispatchEventAndSendReplyPK6AEDescPS_ + 31
65 AE 0x00007fff819e5f04 aeProcessAppleEvent + 288
66 HIToolbox 0x00007fff84ba4af9 AEProcessAppleEvent + 55
67 AppKit 0x00007fff89c52394 _DPSNextEvent + 2245
68 AppKit 0x00007fff89c5132a -[NSApplication _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 454
69 AppKit 0x00007fff89c45e84 -[NSApplication run] + 682
70 AppKit 0x00007fff89c0f46c NSApplicationMain + 1176
71 Unity 0x0000000101c56108 _Z10EditorMainiPPKc + 1368
72 Unity 0x0000000101c567b9 main + 9
73 Unity 0x0000000100001cd4 start + 52

Debug info from gdb:

=================================================================
Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================