Editor crashes on second play

I'm using Steamworks.NET on OSX and its been working fine until recently, the Editor will hard crash immediately when hitting play a second time. I haven't done any recent script changes, and the most recent Steam related work I did was achievement hooks, which wrapped up without issues. It sounds to me like something in the plugin is not unloading correctly when the Editor stops playing. I can currently bypass it by keeping Steam closed, while the plugin throws some errors the project works fine.

Here are the most recent entries in Editor.log:

 Receiving unhandled NULL exception
 Obtained 43 stack frames.
 #0  0x0000014be9b7fe in OSXHelpers::CIOPollingHelper::Register(unsigned long, OSXHelpers::CIOPollingHelper::IHelperCallback*, int)
 #1  0x0000014b4eddd3 in CCrossProcessPipe::BConnectToPipe(char const*, bool, unsigned int, unsigned int, unsigned int)
 #2  0x0000014b4eb281 in CClientPipe::BConnect(char const*, bool, int, unsigned int, unsigned int, unsigned int)
 #3  0x0000014b4e20aa in CIPCClient::CreateIPCPipe(char const*, bool, bool)
 #4  0x0000014b8f5c35 in CSteamClient::CreateSteamPipeInternal(bool)
 #5  0x0000012d067377 in SteamAPI_Init
 #6  0x0000012c9c1477 in Init
 #7  0x0000012bc80abe in  (wrapper managed-to-native) Steamworks.NativeMethods:SteamAPI_Init () + 0xbe (0x12bc80a00 0x12bc80b0e) [0x10d587660 - Unity Child Domain]
 #8  0x0000012bc809b0 in  Steamworks.SteamAPI:Init () + 0x80 (0x12bc80930 0x12bc809f1) [0x10d587660 - Unity Child Domain]
 #9  0x0000012bc80214 in  SteamManager:Awake () + 0x5d4 (0x12bc7fc40 0x12bc8030a) [0x10d587660 - Unity Child Domain]
 #10 0x0000012251d38a in  (wrapper runtime-invoke) object:runtime_invoke_void__this__ (object,intptr,intptr,intptr) + 0xfa (0x12251d290 0x12251d4bd) [0x10d587660 - Unity Child Domain]
 #11 0x0000010aa8785e in mono_get_runtime_build_info
 #12 0x0000010abb211e in mono_runtime_invoke
 #13 0x00000101dee24d in ScriptingInvocation::Invoke(MonoException**, bool)
 #14 0x00000101dee153 in ScriptingInvocation::InvokeChecked(MonoException**)
 #15 0x00000102293649 in MonoBehaviour::CallMethodInactive(ScriptingMethodMono)
 #16 0x00000102297be6 in MonoBehaviour::AddToManager()
 #17 0x000001022976b3 in MonoBehaviour::AwakeFromLoad(AwakeFromLoadMode)
 #18 0x00000101dfe9d6 in AwakeFromLoadQueue::InvokePersistentManagerAwake(AwakeFromLoadQueue::Item*, unsigned int, AwakeFromLoadMode)
 #19 0x00000101dadcbf in LoadSceneOperation::CompleteAwakeSequence()
 #20 0x00000101dacf77 in LoadSceneOperation::IntegrateMainThread()
 #21 0x00000101daeb39 in PreloadManager::UpdatePreloadingSingleStep(PreloadManager::UpdatePreloadingFlags, int)
 #22 0x00000101daf57f in PreloadManager::WaitForAllAsyncOperationsToComplete()
 #23 0x00000102327cd2 in EditorSceneManager::RestoreSceneBackups(std::vector<EditorSceneManager::SceneBackup, stl_allocator<EditorSceneManager::SceneBackup, (MemLabelIdentifier)94, 16> >&, EditorSceneManager::PlayModeChange, bool)
 #24 0x000001026440ea in Application::EnterPlayMode(bool)
 #25 0x0000010264091c in Application::SetIsPlaying(bool)
 #26 0x0000010264022d in Application::TickTimer()
 #27 0x007fff8f598f3f in __NSFireTimer
 #28 0x007fff8db0fd04 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__
 #29 0x007fff8db0f98f in __CFRunLoopDoTimer
 #30 0x007fff8db0f4ea in __CFRunLoopDoTimers
 #31 0x007fff8db06c31 in __CFRunLoopRun
 #32 0x007fff8db061c4 in CFRunLoopRunSpecific
 #33 0x007fff8d067ebc in RunCurrentEventLoopInMode
 #34 0x007fff8d067cf1 in ReceiveNextEventCommon
 #35 0x007fff8d067b26 in _BlockUntilNextEventMatchingListInModeWithFilter
 #36 0x007fff8b602e24 in _DPSNextEvent
 #37 0x007fff8bd7e85e in -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:]
 #38 0x007fff8b5f77ab in -[NSApplication run]
 #39 0x007fff8b5c21de in NSApplicationMain
 #40 0x000001026e4128 in EditorMain(int, char const**)
 #41 0x000001026e4939 in main
 #42 0x00000100002604 in start
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