the $ancient_browser variables did not treat as an ancient browser
listed in modern_browser, but has lower version

src/http/modules/ngx_http_browser_module.c

diff --git a/src/http/modules/ngx_http_browser_module.c b/src/http/modules/ngx_http_browser_module.c
index 083375b..390b62f 100644
--- a/src/http/modules/ngx_http_browser_module.c
+++ b/src/http/modules/ngx_http_browser_module.c
@@ -339,6 +339,8 @@
             if (version >= modern[i].version) {
                 return NGX_HTTP_MODERN_BROWSER;
             }
+
+            return NGX_HTTP_ANCIENT_BROWSER;
         }
 
         if (!cf->modern_unlisted_browsers) {