What is the label for /etc/passwd and /etc/shadow, this may be
unrelated but
I have experienced a similar issue and the /etc/shadow was not labelled
correctly by SELinux.
after relabeling I have:
# ls -Z /etc/{passwd,shadow}
unconfined_u:object_r:passwd_file_t:s0 /etc/passwd
unconfined_u:object_r:shadow_t:s0 /etc/shadow
This is strange because on another F26 computer, I have that:
system_u:object_r:passwd_file_t:s0 /etc/passwd
system_u:object_r:shadow_t:s0 /etc/shadow
Frédéric