KVM with VirtioFS on host, Windows Server guest, VirtioFS access denied

I have some successful setups of Linux guests under KVM with VirtioFS, even able to boot from theese folders without any "classical" drive images or dedicated partitions.

Now, I have a need run a Windows Server guest, and share files from it with the host. I've read that VirtioFS is supported on Windows guests, so I've installed WinFSP (as per this manual), theese drivers (which have support for VirtioFS), the Z: drive even appeared... But that's all. When attempting to access it - I just get an "Access Denied" error and no access to the underlying VirtioFS filesystem.

Things I've tried:

1. chmoding 777 the target folder - no changes
2. Fiddling around with virtiofsd command line arguments - no changes
3. Trying to run the virtiofs.exe on the guest manually - It just crashes on attempting to access the Z: drive for no apparent reason (although seems to work fine when running as an autostartable service)
4. Trying both virtiofsd host demons - rust one and C one. The C one tends to crash for weird reasons...

I'm a bit of at loss about what to do now. The same setup (with the rust demon) works just fine with Linux.

What am I doing wrong?

UPD: for some reason, each and every request on the guest (while running virtiofs.exe -d -1 -D - directly) ends up with an error BytesReturned != hdr->len, Bytes returned: 0, Expected: xxx.