NOAUTH errors in WP error log

I apologise if this is the wrong place to post as I doubt there’s an error in the plugin but hope the solution is so obvious I won’t be wasting much of your time…

I am attempting to implement a redis cache on my WorPress sites (specifically those running WooCommerce). The server is running nginx & mariadb, csf firewall & the website is using Divi as the theme and has Wordfence running.
I have installed Redis server

• It’s bound only to localhost:
  bind 127.0.0.1 -::1
• It’s got protected mode on:
  protected-mode yes
• and has require password set
  requirepass *******************

I can connect to it with redis-cli using AUTH <password> and it responds to ping with PONG

In the csf firewall there is no entry for the redis port (left at default 6379), in other words I am confident there is no possibility of remote bad guys issuing direct calls to redis.
TCP_IN = “20,21,22,25,53,853,80,123,443,10000,22222,49900:49999”

In the WordPress site I have the password in the wp-config file:
define( ‘WP_REDIS_PREFIX’, ‘<site>.net.au:’ );
define( ‘WP_REDIS_DISABLE_BANNERS’, true );
define(‘WP_REDIS_PASSWORD’, ‘**********);    (I have double-triple checked, the password matches!)

The Redis Object Cache plugin is installed, it shows the cache as operational:

The diagnostics look OK to me:

https://repository.epicsites.com.au/Redis_OC_Diags.txt

and the Redis Object Cache in the dashboard is reporting sensible looking activity:

Here’s the problem: every time I browse the site I get heaps of errors in the log:

redis sent invalid response: “-NOAUTH Authentication required.” while reading response header from upstream client:111.111.111.111, server: xxxx.net.au, request: “GET / HTTP/2.0”, subrequest: “/redis-fetch”, upstream: “redis://127.0.0.1:6379”, host: xxxx.net.au
(the IP address matches the public IP of my home office, so I know these are genuine attempts to access redis via the website.)

I’m at a complete loss, what have I done wrong that causes requests to be sent to redis without passing the AUTH password? I’ve googled a lot and found nothing helpful, I’m hoping you can spare the time to look at this.
Thanks, Graham

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