Currently, as of sys-apps/portage-18.104.22.168, env-update only reports the name of a file which it could not open if the failure was due to a permission problem, other errors do not include such information. Reporting the names of files which are unavailable for other reasons could be useful in determining why an error occurred.
Created attachment 160021 [details, diff]
show the file path when an error occurs
This should make it easier to debug problems like those reported.
This is fixed in 2.2_rc2.