A couple of years ago, I encountered the dreaded “Cubase hang on project close” problem. The culprit is usually a plugin. But how to find out? In this case, start WinDbg, but Select “File->Attach to Process” and then select Cubase. Do this when you already closed the project and Cubase hangs. Now just type “k” in the command window. You then get a stack trace, which can be really long. In there, search for a plugin name that you used in the project. Most likely, this is the culprit for the hang.
0 Id: 1330.2120 Suspend: 1 Teb: 00000000`002af000 Unfrozen
# Child-SP RetAddr Call Site
00 00000000`0014e6c8 00007ffc`080a9252 ntdll!NtWaitForSingleObject+0x14
01 00000000`0014e6d0 00007ffb`c8bc8c7d KERNELBASE!WaitForSingleObjectEx+0xa2
02 00000000`0014e770 00007ffb`c891e576 D3D10Warp!ThreadPool::WaitWhileBusy+0xdd
03 00000000`0014e7f0 00007ffb`c88f307d D3D10Warp!UMContext::FlushAllRenderingTasks+0xfc6
04 00000000`0014f090 00007ffc`04f61451 D3D10Warp!UMDevice::DestroyResource+0x44d
05 00000000`0014f160 00007ffc`04f60b05 d3d11!CResource<ID3D11Buffer>::CLS::FinalRelease+0x71
06 00000000`0014f190 00007ffc`04f7c34c d3d11!TCLSWrappers<CBuffer>::CLSDestroy+0x15
07 00000000`0014f1c0 00007ffc`04f7c2f9 d3d11!CLayeredObjectWithCLS<CBuffer>::~CLayeredObjectWithCLS<CBuffer>+0x24
08 00000000`0014f1f0 00007ffc`04f7d17a d3d11!CLayeredObjectWithCLS<CBuffer>::Release+0x9
09 00000000`0014f220 00007ffc`04f6771f d3d11!NDXGI::CDeviceChild<IDXGIResource1,IDXGISwapChainInternal>::FinalRelease+0x12a
0a 00000000`0014f260 00007ffc`04f68279 d3d11!CUseCountedObject<NOutermost::CDeviceChild>::UCDestroy+0x27f
0b 00000000`0014f290 00007ffc`04f7e29b d3d11!NOutermost::CDevice::FlushDeletionPool+0x369
0c 00000000`0014f320 00007ffc`04f6b100 d3d11!CDevice::LLOBeginLayerDestruction+0x10f
0d 00000000`0014f350 00007ffc`04f67ef5 d3d11!NDXGI::CDevice::LLOBeginLayerDestruction+0x10c
0e 00000000`0014f3a0 00007ffc`04f67dab d3d11!NOutermost::CDevice::LLOBeginLayerDestruction+0x25
0f 00000000`0014f3d0 00007ffc`04f67cf4 d3d11!TComObject<NOutermost::CDevice>::~TComObject<NOutermost::CDevice>+0x23
10 00000000`0014f400 00007ffc`04f67d74 d3d11!TComObject<NOutermost::CDevice>::`scalar deleting destructor'+0x14
11 00000000`0014f430 00007ffc`04fa84bb d3d11!TComObject<NOutermost::CDevice>::Release+0x44
12 00000000`0014f460 00007ffc`04f64934 d3d11!ATL::CComPtr<IUnknown>::~CComPtr<IUnknown>+0x4b
13 00000000`0014f4a0 00007ffc`05327735 d3d11!CLayeredObjectWithCLS<CBuffer>::CContainedObject::Release+0x2c4
14 00000000`0014f4f0 00007ffc`0535f929 d2d1!CHwSurfaceRenderTargetSharedData::~CHwSurfaceRenderTargetSharedData+0x1f5
15 00000000`0014f520 00007ffc`0535f9d7 d2d1!InitializableObject<RefCountedObject<CD3DDeviceLevel1,LockingRequired,DeleteOnZeroReference> >::`vector deleting destructor'+0x29
16 00000000`0014f550 00007ffc`0535fead d2d1!RefCountedObject<CD3DDeviceLevel1,LockingRequired,DeleteOnZeroReference>::Release+0x47
17 00000000`0014f580 00007ffc`0535e7c9 d2d1!CD3DDeviceManager::D3DDeviceInformation::`scalar deleting destructor'+0x2d
18 00000000`0014f5b0 00007ffc`052bfb34 d2d1!CD3DDeviceManager::~CD3DDeviceManager+0x71
19 00000000`0014f5e0 00007ffc`05300a00 d2d1!D2DFactory::~D2DFactory+0xbc
1a 00000000`0014f620 00007ffc`053009e9 d2d1!RefCountedObject<D2DFactoryLocking<MultiThreadedTrait>,LockingRequired,DeleteOnZeroReference>::`vector deleting destructor'+0x14
*** WARNING: Unable to verify checksum for C:\Program Files\Vstplugins\ToneBoosters\TrackEssentials_v3\TB_Compressor_v3.dll
*** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\Program Files\Vstplugins\ToneBoosters\TrackEssentials_v3\TB_Compressor_v3.dll -
1b 00000000`0014f650 00007ffb`bb104c7a d2d1!RefCountedObject<D2DFactoryLocking<MultiThreadedTrait>,LockingRequired,DeleteOnZeroReference>::Release+0x39
1c 00000000`0014f680 00007ffc`08401243 TB_Compressor_v3!VSTPluginMain+0x4390a
1d 00000000`0014f6c0 00007ffc`08401017 ucrtbase!<lambda_f03950bc5685219e0bcd2087efbe011e>::operator()+0xc3
1e 00000000`0014f720 00007ffc`08400fd4 ucrtbase!__crt_seh_guarded_call<int>::operator()<<lambda_7777bce6b2f8c936911f934f8298dc43>,<lambda_f03950bc5685219e0bcd2087efbe011e> & __ptr64,<lambda_3883c3dff614d5e0c5f61bb1ac94921c> >+0x3b
1f 00000000`0014f750 00007ffb`bb127bae ucrtbase!execute_onexit_table+0x34
20 00000000`0014f780 00007ffb`bb127cac TB_Compressor_v3!VSTPluginMain+0x6683e
21 00000000`0014f7b0 00007ffc`0b9c4063 TB_Compressor_v3!VSTPluginMain+0x6693c
22 00000000`0014f810 00007ffc`0b9cff81 ntdll!LdrpCallInitRoutine+0x6b
23 00000000`0014f880 00007ffc`0b9cf5ae ntdll!LdrpProcessDetachNode+0xf5
24 00000000`0014f950 00007ffc`0b9cf955 ntdll!LdrpUnloadNode+0x3e
25 00000000`0014f9a0 00007ffc`0b9cf8d3 ntdll!LdrpDecrementModuleLoadCountEx+0x71
26 00000000`0014f9d0 00007ffc`0808bced ntdll!LdrUnloadDll+0x93
*** WARNING: Unable to verify checksum for C:\Program Files\Steinberg\Cubase 9.5\Components\VSTPlugManager.dll
*** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\Program Files\Steinberg\Cubase 9.5\Components\VSTPlugManager.dll -
27 00000000`0014fa00 00000000`155b6f4a KERNELBASE!FreeLibrary+0x1d
28 00000000`0014fa30 00000000`155b803c VSTPlugManager!InitDll+0x330fb
29 00000000`0014fa70 00000000`155b0105 VSTPlugManager!InitDll+0x341ed
2a 00000000`0014faa0 00007ffc`0b37786d VSTPlugManager!InitDll+0x2c2b6
2b 00000000`0014fad0 00007ffc`0b3767f8 USER32!UserCallWinProc+0x25d
*** ERROR: Module load completed but symbols could not be loaded for C:\Program Files\Steinberg\Cubase 9.5\Cubase9.5.exe
2c 00000000`0014fc50 00000001`41bf910d USER32!DispatchMessageWorker+0x2a8
2d 00000000`0014fce0 00000001`41dbf51d Cubase9_5+0x1bf910d
2e 00000000`0014fd10 00000001`41dbf459 Cubase9_5+0x1dbf51d
2f 00000000`0014fd40 00000001`41be441c Cubase9_5+0x1dbf459
30 00000000`0014fd70 00000001`419488c4 Cubase9_5+0x1be441c
31 00000000`0014fda0 00000001`41947f51 Cubase9_5+0x19488c4
32 00000000`0014fde0 00000001`4194b60f Cubase9_5+0x1947f51
33 00000000`0014fee0 00000001`41efe022 Cubase9_5+0x194b60f
34 00000000`0014ff20 00007ffc`0b2b3034 Cubase9_5+0x1efe022
35 00000000`0014ff60 00007ffc`0ba01471 KERNEL32!BaseThreadInitThunk+0x14
36 00000000`0014ff90 00000000`00000000 ntdll!RtlUserThreadStart+0x21
(This is an old excerpt from C9.5 . The problem was the TB_Compressor_V3 plugin, which was built with an older version of the VSTGUI SDK which contained a bug. The dev switched to a newer version and the problem was gone. )