/etc/nsswitch.conffile is read exactly once by the first process of a Cygwin process tree.
If there was no
/etc/nsswitch.conffile when this first process started, then no other process in the running Cygwin process tree will try to read the file.
If you create or change
/etc/nsswitch.conf, you have to restart all Cygwin processes that need to see the change.
If the process you want to see the change is a child of another process, you need to restart all of that process's parents, too.