Comment 1 for bug 1845284

This sounds like more of a libguestfs issue than a nova issue, unless nova isn't creating the guest in such a way that libguestfs would cleanup properly.

What version of libguestfs are you using?

Also note that file injection as a feature is disabled by default (it has been for years) and is also deprecated in the API:

https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#id52

So in all this is very low priority to resolve IMO.