The driver (control surface via MIDI) is hung and reaper is waiting for it to close the midi comm to close out and clean up. Since it is in kernel (OS code), if it never releases you likely have to reboot since that's the only way to clear up the hang down in the OS code.
00 00000000`0012e768 000007fe`fcae3e36 ntdll!ZwDeviceIoControlFile+0xa <=====
01 00000000`0012e770 00000000`76c45cdf KERNELBASE!DeviceIoControl+0x18e06
02 00000000`0012e7e0 000007fe`fa2369dc kernel32!DeviceIoControlImplementation+0x7f
03 00000000`0012e830 000007fe`fa236b97 wdmaud!SyncIoctl+0xc0
04 00000000`0012e8d0 000007fe`fa225f3f wdmaud!PinSetState+0x5f
05 00000000`0012e940 000007fe`fa223d9c wdmaud!CMIDIDeviceBase::CloseMidiPin+0x1f <=======
06 00000000`0012e970 000007fe`fa23a07b wdmaud!CMIDIOutDevice::`vector deleting destructor'+0x2c
07 00000000`0012e9b0 000007fe`fa2372ca wdmaud!_chkstk+0x20eb
08 00000000`0012e9f0 000007fe`fa237593 wdmaud!CRT_INIT+0x96
09 00000000`0012ea40 00000000`76d8778b wdmaud!CRT_INIT+0x35f
0a 00000000`0012eba0 00000000`76d8c1e0 ntdll!LdrShutdownProcess+0x1db
0b 00000000`0012ecc0 00000001`4037275f
ntdll!RtlExitUserProcess+0x90 <==== reaper shutting down and this is the transition to kernel code
0c 00000000`0012ecf0 00000001`407c0c11 reaper+0x37275f
0d 00000000`0012fea0 00000000`76c459cd reaper+0x7c0c11
0e 00000000`0012ff60 00000000`76da385d kernel32!BaseThreadInitThunk+0xd
Here's a deeper explanation but most likely driver related..
https://blogs.technet.microsoft.com/...ble-processes/
Either way, that's the issue, outstading driver call not being serviced/answered so it can complete the process shutdown which is preventing reaper from exiting. I noticed wdmaudio, not sure if switching that is possible or will workaround the issue. That's also why it hangs when starting a 2nd reaper process, the hardware is already tied up. You could unplug/re-plugin the hardware when this occurs, it'll either do nothing, force it to release, or BSOD the box.