[libvirt] 5.6.0 regression: "Some activation file descriptors are unclaimed"

[Allen, John]

After upgrading to v5.6.0, starting libvirtd fails with the following message
in journalctl -xe:

libvirtd[186338]: internal error: Some activation file descriptors are unclaimed

5b8569dd6e284b9159c701e8bffafb196983fc4a introduces the message. The commit
message indicates that systemd version 227 is required, but my system seems to
be running version 237.

Is this a known issue? Is there any other configuration for systemd needed to
avoid the problem?

Thanks,
John