Are you requesting subsequent resource loading in the backend?

If so, try specifying sub_filter

example

location /wiremock/__admin {
    rewrite ^/wiremock(.*)$ $1 break;
    proxy_pass https://localhost:7443/__admin;
    proxy_set_header Host $host;
    sub_filter '/__admin' '/wiremock/__admin';
    sub_filter_once off;
    proxy_set_header Accept-Encoding ""; 
}

sub_filter will replace all response bodies from the backend, so be careful not to make unintended matches.

http://nginx.org/en/docs/http/ngx_http_sub_module.html

I think the best way to fix it is to specify resource loading that matches the front.