As I still have this problem, I’m gonna bump this thread 
By taking memory dumps in the deadlock state and looking at a threaddump in windbg, I’ve narrowed the problem down to the following plugins
Shattered Glass audio’s SGA1566 and Tonebooster’s plugins (the v3 ones, not the JUCE ones).
I think this is the thread where it somehow goes wrong:
0 Id: 371c.4908 Suspend: 1 Teb: 00000000`00234000 Unfrozen
# Child-SP RetAddr Call Site
00 00000000`0014e818 00007ff9`332d9252 ntdll!NtWaitForSingleObject+0x14
01 00000000`0014e820 00007ff8`dbd08c7d KERNELBASE!WaitForSingleObjectEx+0xa2
02 00000000`0014e8c0 00007ff8`dba5e576 D3D10Warp!ThreadPool::WaitWhileBusy+0xdd
03 00000000`0014e940 00007ff8`dba2cba6 D3D10Warp!UMContext::FlushAllRenderingTasks+0xfc6
04 00000000`0014f1e0 00007ff8`dba2ac38 D3D10Warp!UMDevice::Destroy+0xb6
05 00000000`0014f2c0 00007ff8`dba38185 D3D10Warp!UMDevice::`vector deleting destructor'+0x28
06 00000000`0014f300 00007ff9`2ff20b7c D3D10Warp!UMDevice::DestroyDevice+0x55
07 00000000`0014f340 00007ff9`2ff233b8 d3d11!NDXGI::CDevice::DestroyDriverInstance+0x5c
08 00000000`0014f3a0 00007ff9`2ff1763a d3d11!CContext::LUCBeginLayerDestruction+0x7c
09 00000000`0014f3f0 00007ff9`2ff17982 d3d11!CUseCountedObject<NOutermost::CDeviceChild>::UCDestroy+0x19a
0a 00000000`0014f420 00007ff9`2ff2e2ab d3d11!CUseCountedObject<NOutermost::CDeviceChild>::UCReleaseUse+0xb2
0b 00000000`0014f450 00007ff9`2ff1b100 d3d11!CDevice::LLOBeginLayerDestruction+0x11f
0c 00000000`0014f480 00007ff9`2ff17ef5 d3d11!NDXGI::CDevice::LLOBeginLayerDestruction+0x10c
0d 00000000`0014f4d0 00007ff9`2ff17dab d3d11!NOutermost::CDevice::LLOBeginLayerDestruction+0x25
0e 00000000`0014f500 00007ff9`2ff17cf4 d3d11!TComObject<NOutermost::CDevice>::~TComObject<NOutermost::CDevice>+0x23
0f 00000000`0014f530 00007ff9`2ff17d74 d3d11!TComObject<NOutermost::CDevice>::`scalar deleting destructor'+0x14
10 00000000`0014f560 00007ff9`2ff584bb d3d11!TComObject<NOutermost::CDevice>::Release+0x44
11 00000000`0014f590 00007ff9`2ff14934 d3d11!ATL::CComPtr<IUnknown>::~CComPtr<IUnknown>+0x4b
12 00000000`0014f5d0 00007ff9`302b0921 d3d11!CLayeredObjectWithCLS<CBuffer>::CContainedObject::Release+0x2c4
13 00000000`0014f620 00007ff9`302f4859 d2d1!CHwSurfaceRenderTargetSharedData::~CHwSurfaceRenderTargetSharedData+0x1f5
14 00000000`0014f650 00007ff9`302f4907 d2d1!InitializableObject<RefCountedObject<CD3DDeviceLevel1,LockingRequired,DeleteOnZeroReference> >::`vector deleting destructor'+0x29
15 00000000`0014f680 00007ff9`302f4ed9 d2d1!RefCountedObject<CD3DDeviceLevel1,LockingRequired,DeleteOnZeroReference>::Release+0x47
16 00000000`0014f6b0 00007ff9`302f3991 d2d1!CD3DDeviceManager::D3DDeviceInformation::`scalar deleting destructor'+0x2d
17 00000000`0014f6e0 00007ff9`302709f4 d2d1!CD3DDeviceManager::~CD3DDeviceManager+0x71
18 00000000`0014f710 00007ff9`302b58d0 d2d1!D2DFactory::~D2DFactory+0xbc
19 00000000`0014f750 00007ff9`302b58b9 d2d1!RefCountedObject<D2DFactoryLocking<MultiThreadedTrait>,LockingRequired,DeleteOnZeroReference>::`vector deleting destructor'+0x14
*** WARNING: Unable to verify checksum for C:\Program Files\Vstplugins\!Guitar\SGA1566.dll
*** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\Program Files\Vstplugins\!Guitar\SGA1566.dll -
1a 00000000`0014f780 00000000`7f47695a d2d1!RefCountedObject<D2DFactoryLocking<MultiThreadedTrait>,LockingRequired,DeleteOnZeroReference>::Release+0x39
1b 00000000`0014f7b0 00000000`7f5e59b3 SGA1566+0x5695a
1c 00000000`0014f7f0 00000000`7f5dcf4e SGA1566!VSTPluginMain+0x164463
1d 00000000`0014f860 00000000`7f5dd117 SGA1566!VSTPluginMain+0x15b9fe
1e 00000000`0014f890 00007ff9`36f04053 SGA1566!VSTPluginMain+0x15bbc7
1f 00000000`0014f900 00007ff9`36f0ff71 ntdll!LdrpCallInitRoutine+0x6b
20 00000000`0014f970 00007ff9`36f0f59e ntdll!LdrpProcessDetachNode+0xf5
21 00000000`0014fa40 00007ff9`36f0f945 ntdll!LdrpUnloadNode+0x3e
22 00000000`0014fa90 00007ff9`36f0f8c3 ntdll!LdrpDecrementModuleLoadCountEx+0x71
23 00000000`0014fac0 00007ff9`332bbced 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 -
24 00000000`0014faf0 00000000`19256f3a KERNELBASE!FreeLibrary+0x1d
25 00000000`0014fb20 00000000`192572c0 VSTPlugManager!InitDll+0x330eb
...
*** ERROR: Module load completed but symbols could not be loaded for C:\Program Files\Steinberg\Cubase 9.5\Cubase9.5.exe
2a 00000000`0014fc30 00000001`418f6c4f VSTPlugManager!InitDll+0xc6d9
2b 00000000`0014fc60 00000001`418fc014 Cubase9_5+0x18f6c4f
...
35 00000000`0014ff60 00007ff9`36f41461 KERNEL32!BaseThreadInitThunk+0x14
36 00000000`0014ff90 00000000`00000000 ntdll!RtlUserThreadStart+0x21
Other times, it’s
*** 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 00007ff9`09344c7a d2d1!RefCountedObject<D2DFactoryLocking<MultiThreadedTrait>,LockingRequired,DeleteOnZeroReference>::Release+0x39
1c 00000000`0014f680 00007ff9`33a31243 TB_Compressor_v3!VSTPluginMain+0x4390a
or other TB plugins.
I’ve opened a call at Tonebooster’s, Jeroen was very quick to answer, but sadly cannot reproduce the problem (well, I don’t know yet how to exactly reproduce it, except work for some longer time on a project with the mentioned plugins and then close it…)
I’ve opened calls at Steinberg, but so far all they did was put the blame on a third party plugin (the wrong one).
This problem happened so far with all updates of C9.5 and all revisions of TB plugins this year.
Can i really be the only one with this problem???