Odd config issue, cannot set log_min_duration_statement

All;

I have a client running PostgreSQL v10

I set:

log_min_duration_statement = 0

and restarted the cluster but if I connect via psql and check it's still disabled

postgres=# show log_min_duration_statement ;
 log_min_duration_statement
----------------------------
 -1
(1 row)

I tried an alter system, now if I cat the auto.conf file i see:

$ cat postgresql.auto.conf
# Do not edit this file manually!
# It will be overwritten by the ALTER SYSTEM command.
log_min_duration_statement = '0'

However even after another restart It's still disabled:

postgres=# show log_min_duration_statement ;
 log_min_duration_statement
----------------------------
 -1
(1 row)

I grep'ed for the setting in the config file just in case:

$ grep log_min_duration_statement postgresql.conf
log_min_duration_statement = 0          # -1 is disabled, 0 logs all statements

I'm stumped... Thoughts?

Thanks in advance