I have hundrerds of these in my engintron log
2024/04/18 03:18:46 [error] 859674#859674: *70490 no "charset_map" between the charsets "iso-8859-1" and "utf-8" while reading response header from upstream, client: ::ffff:216.244.66.246, server: localhost, request: "GET /robots.txt HTTP/1.1", subrequest: "/robots.txt", upstream: "http://[2404:f780:4:857::]:8080/robots.txt", host: "moretonbayartscouncil.org"
2024/04/18 03:19:34 [error] 859674#859674: *70576 no "charset_map" between the charsets "iso-8859-1" and "UTF-8" while reading response header from upstream, client: ::ffff:66.249.79.33, server: localhost, request: "GET /ads.txt HTTP/1.1", subrequest: "/ads.txt", upstream: "http://45.248.77.243:8080/ads.txt", host: "tradeshack.au"
2024/04/18 03:38:41 [error] 859674#859674: *72877 no "charset_map" between the charsets "iso-8859-1" and "UTF-8" while reading response header from upstream, client: ::ffff:35.237.159.74, server: localhost, request: "GET /robots.txt HTTP/1.0", subrequest: "/robots.txt", upstream: "http://45.248.77.243:8080/robots.txt", host: "www.abovebeyonddogtraining.com.au"

I have made some changes to common_http.conf which I hoped would make it go away.

location = /robot.txt {
try_files $uri =404;
}

But no luck. I am not sure if this has been reported before... if it has my appologies... but it is driving me bonkers.

Thanks
H