Although you’ve configured Redis to use a host name and port it usually might switch to a socket connection as soon as “localhost” is used. So it would be worse to check under which user the daemon is running and how it has been set-up.
the Redis configuration (/etc/redis/redis.conf) might look similar to this:
port 6379
bind 127.0.0.1
unixsocket /var/run/redis.sock
unixsocketperm 0770
The Nextcloud configuration might look like this:
'redis' => array (
'host' => '/var/run/redis.sock',
'port' => 0,
'timeout' => 0.0,
),
See also: