Looking glass ivshmemOpen DeviceIoControl Failed: device was already attached to another device (0x00000224)

I have setup a KVM win10 guest with gpu passthrough, as well as looking glass with IVSHMEM Device driver.

In fact it functioned well a few month ago. But when I tried to launch it recently looking glass host failed to start. The error message in looking-glass-host is quite clear:

[I]    435396798               app.c:771  | app_main                       | Looking Glass Host (B6)
[I]    435397196           cpuinfo.c:37   | lgDebugCPU                     | CPU Model: AMD Ryzen 7 5700G with Radeon Graphics
[I]    435397594           cpuinfo.c:38   | lgDebugCPU                     | CPU: 1 sockets, 8 cores, 8 threads
[I]    435399688           ivshmem.c:132  | ivshmemInit                    | IVSHMEM 0* on bus 0x3, device 0x1, function 0x0
   435401944 [E]            ivshmem.c:214  | ivshmemOpen                    | DeviceIoControl Failed: 0x00000224 (An attempt was made to attach to a device that was already attached to another device.)
[E]    435402565               app.c:783  | app_main                       | Failed to open the IVSHMEM device

It points out that my IVSHMEM device has already been attached to another device. But I am now stuck here with no clue how to solve this. I am connecting to the guest VM via RDP, but I don’ t think this is causing the problem because last time when looking glass worked I was also connecting via RDP.

Trying to run looking glass guest would stuck at starting session after successfully handshaking with the host:

[I]  17262411821              main.c:1566 | lg_run                         | Guest Information:
[I]  17262411837              main.c:1567 | lg_run                         | Version  : B6
[I]  17262411841              main.c:1588 | lg_run                         | UUID     : 54e36575-f3d6-45fb-8329-0c776ee4318c
[I]  17262411846              main.c:1597 | lg_run                         | CPU Model: AMD Ryzen 7 5700G with Radeon Graphics
[I]  17262411850              main.c:1598 | lg_run                         | CPU      : 1 sockets, 8 cores, 8 threads
[I]  17262411852              main.c:1600 | lg_run                         | Using    : DXGI Direct3D 11
[I]  17262411854              main.c:1636 | lg_run                         | OS       : Windows
[I]  17262411855              main.c:1638 | lg_run                         | OS Name  : Windows 10 Pro (Build: 19045) 
[I]  17262411858              main.c:1660 | lg_run                         | Starting session

You either have another LG host application running or some other application that uses IVSHMEM and is using it. One application that is commonly notorious to interfere with LG is the SCREAM sound system. If you use SCREAM, please don’t.

Went through task manager, found nothing likely to use IVSHMEM. But then I tried to disable IVSHMEM device and re-enable it after a reboot, and now LG worked again. Not sure whether it will still work on next boot though.