Nginx regex match variables not working in lua blocks

NGX_VERSION='1.16.1'
LUAJIT_VERSION='2.1-20190912'
LUAJIT_MAJOR_VERSION='2.1'
NGX_DEVEL_KIT_VERSION='0.3.0'
LUA_NGINX_MODULE_VERSION='0.10.15'
LUA_RESTY_CORE_VERSION='0.1.17'
LUA_RESTY_LRUCACHE_VERSION='0.09'

URL:- http://example.com/sess1234/phpmyadmin/index.php

location ~ /phpmyadmin {
   root /usr/local/nginx;
   rewrite /sess([a-z0-9]+)/(wordpress|phpmyadmin)(.*) /$2$3;
   default_type 'text/plain';

   set $var1 $1;
   set $wp "valuewp";

   content_by_lua_block {
      ngx.say(ngx.var.var1)
      ngx.say(ngx.var.wp)
   }

   #return 200 "var1 = $var1 and wp = $wp";
}

Above code output
(ngx.var.var1 is empty here, ) I'm expecting it should be 1234
valuewp

when #return... is uncommented output is
-- var1 = 1234 and wp = valuewp

Start with the reproduced Nginx configuration and the content_by_lua_block entry point, then compare ngx.var.var1 with the commented return output for the same rewritten URL. Reproduce the difference using the stated Nginx, LuaJIT, and module versions; done means the regex-derived value is available in the Lua block as shown by the expected output.