qemu 4.2 segfaults on VF detach

After updating Ubuntu 20.04 to the Beta version, we get the following error and the virtual machines stucks when detaching PCI devices using virsh command: 

Error:
error: Failed to detach device from /tmp/vf_interface_attached.xml
error: internal error: End of file from qemu monitor

steps to reproduce:
 1. create a VM over Ubuntu 20.04 (5.4.0-14-generic)
 2. attach PCI device to this VM (Mellanox VF for example)
 3. try to detaching  the PCI device using virsh command:
   a. create a pci interface xml file:
        
      <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
      <address type='pci' domain='0x0000' bus='0x11' slot='0x00' function='0x2' />
      </source>
      </hostdev>
    
   b.  #virsh detach-device <VM-Doman-name> <pci interface xml file>



- Ubuntu release:
  Description:    Ubuntu Focal Fossa (development branch)
  Release:        20.04

- Package ver:
  libvirt0:
  Installed: 6.0.0-0ubuntu3
  Candidate: 6.0.0-0ubuntu5
  Version table:
     6.0.0-0ubuntu5 500
        500 http://il.archive.ubuntu.com/ubuntu focal/main amd64 Packages
 *** 6.0.0-0ubuntu3 100
        100 /var/lib/dpkg/status

- What you expected to happen: 
  PCI device detached without any errors.

- What happened instead:
  getting the errors above and he VM stuck

additional info:
after downgrading the libvirt0 package and all the dependent packages to 5.4 the previous, version, seems that the issue disappeared