10 is the default value, as is wal_level = “replica”.
By the way, if you had checked your postgresql-10-main.log after you sent the reload command (always a good idea), it gives exactly this hint as I remember.
I have an issue with WAL settings with postgress 10.1 used for zabbix monitoring system. When i change WAL setting to "minimal" the database goes down. We used this setting in version 9.4 to improve performance of our monitoring server so i would like to replicate this setting.