nginx version: openresty/1.19.9.1
ngx_lua-0.10.20

-- my nginx.conf
worker_processes 1;
user root;
pcre_jit on;

events {
worker_connections 1024;
}

http {
lua_package_path '$prefix/?.lua;$prefix/resty_modules/lualib/?.lua;;';
lua_code_cache off;
default_type text/plain;
keepalive_timeout 65;

server {
    listen 8080;
    location / {
        content_by_lua_file lua/not_found.lua;
    }

    location = /main {
        content_by_lua_file lua/main.lua;
    }

    location = /sub {
        content_by_lua_file lua/sub.lua;
    }

}

}

-- main.lua
local res = ngx.location.capture("/sub")
ngx.say(res.body)
ngx.say("main")

-- sub.lua
ngx.say("sub")

-- question
with lua_code_cache off;
when first issue curl /sub then curl /main
just got subrequest cycle error as follow

stack traceback:
coroutine 0:
[C]: in function 'capture'
/root/study/test/lua/main.lua:1: in main chunk, client: 127.0.0.1, server: , request: "GET /main HTTP/1.1", subrequest: "/sub", host: "localhost:8080"
2022/04/19 01:21:07 [error] 25279#25279: *10 lua subrequests cycle while processing "/sub", client: 127.0.0.1, server: , request: "GET /main HTTP/1.1", subrequest: "/sub", host: "localhost:8080"
2022/04/19 01:21:07 [error] 25279#25279: *10 lua entry thread aborted: runtime error: /root/study/test/lua/main.lua:1: failed to issue subrequest: -1
stack traceback:
coroutine 0:
[C]: in function 'capture'
/root/study/test/lua/main.lua:1: in main chunk, client: 127.0.0.1, server: , request: "GET /main HTTP/1.1", subrequest: "/sub", host: "localhost:8080"

and curl /main just print 51 line "mian" without any "sub"
is this intended ?
and i couldn't figure it out