NGINX 502 Bad Gateway while trying to use cache proxy

FiveM Server Development Server Discussion
1

NGINX kicks out 502 bad gateway while trying to use cache proxy, any idea why that might be?
server.cfg:

adhesive_cdnKey "allahiniTten"
fileserver_add ".*" "http://proxy.xxxx.com/files"

site config:

proxy_cache_path /srv/cache levels=1:2 keys_zone=assets:48m max_size=10g ;

upstream backend {
    server fivemserverip:30120;
}
server {
    listen 80;

    server_name proxy.xxxx.com;

    access_log /var/log/nginx/reverse-access.log;
    error_log /var/log/nginx/reverse-error.log;

    location /files/ {
        proxy_pass http://backend$request_uri;
        add_header X-Cache-Status $upstream_cache_status;
        proxy_cache_lock on;
        proxy_cache assets;
        proxy_cache_valid 1y;
        proxy_cache_key $request_uri$is_args$args;
        proxy_cache_revalidate on;
        proxy_cache_min_uses 1;
    }

}

/var/log/nginx/reverse-access.log:

MYCLIENTIP - - [04/May/2021:16:03:52 -0400] "GET /files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e HTTP/1.1" 502 166 "-" "CitizenFX/1"
MYCLIENTIP - - [04/May/2021:16:04:08 -0400] "GET /files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e HTTP/1.1" 499 0 "-" "CitizenFX/1"
MYCLIENTIP - - [04/May/2021:16:04:14 -0400] "GET /files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e HTTP/1.1" 499 0 "-" "CitizenFX/1"

/var/log/nginx/reverse-error.log:

2021/05/04 16:03:52 [error] 3413#3413: *154 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: MYCLIENTIP, server: proxy.xxxx.com, request: "GET /files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e HTTP/1.1", upstream: "http://fivemserverip:30120/files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e", host: "proxy.xxxx.com"
2021/05/04 16:04:08 [error] 3413#3413: *156 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: MYCLIENTIP, server: proxy.xxxx.com, request: "GET /files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e HTTP/1.1", upstream: "http://fivemserverip:30120/files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e", host: "proxy.xxxx.com"
2021/05/04 16:04:14 [error] 3413#3413: *154 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: MYCLIENTIP, server: proxy.xxxx.com, request: "GET /files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e HTTP/1.1", upstream: "http://fivemserverip:30120/files/sessionmanager/resource.rpf?hash=78327af36a7b5197b0e8996782c33b57e093623e", host: "proxy.xxxx.com"