Lua shutdown double free, lua threads alive during shutdown?

In my Lua C++ integration (Lua 5.3.4) I'm having problems during Lua runtime shutdown. I have an std::unique_ptr which holds the Lua State and I save a collection of states into a std::list which lies in global scope:

using lua_state = std::unique_ptr<lua_State, decltype(lua_close) *>;
std::list<lua_state> ls;

int main(int argc, char** argv)
{
    for (int script = 0; script < 10; ++script)
    {
        const auto L = ls.emplace_back(luaL_newstate(), lua_close).get();

        if (luaL_dofile(L, "test.lua") == 0)
        {
            for (int value = 0; value < 50; ++value)
            {
                auto name = ("TEST" + std::to_string(value));
                lua_pushnumber(L, value);
                lua_setglobal(L, name.c_str());
            }
        }
    }

    // do things with each script

    return 0;
}

I load a bunch of Lua scripts and set a collecion of global values¹, when the program finishes, the ls list is destroyed hence lua_close is called and it ends doing something that looks like a double free.

app.exe!l_alloc(void * ud, void * ptr, unsigned int osize, unsigned int nsize)
app.exe!luaM_realloc_(lua_State * L, void * block, unsigned int osize, unsigned int nsize)
app.exe!freestack(lua_State * L)
app.exe!close_state(lua_State * L)
app.exe!lua_close(lua_State * L)
app.exe!std::unique_ptr<lua_State,void (__cdecl*)(lua_State *)>::~unique_ptr<lua_State,void (__cdecl*)(lua_State *)>()

In the l_alloc function, an exception is thrown in free call:

static void *l_alloc (void *ud, void *ptr, size_t osize, size_t nsize) {
  (void)ud; (void)osize;  /* not used */
  if (nsize == 0) {
    free(ptr);
 // ^^^^^^^^^^ <--- HEAP[app.exe]: Invalid address specified to RtlValidateHeap( 00080000, 000B0D90 )
    return NULL;
  }
  else
    return realloc(ptr, nsize);
}

If I set a breakpoint in the lua_close function and check the state of the stack (lua_gettop) I get a stack of size -6 and checking the types of the values held in the stack I get:

lua_typename(L, lua_type(L, -1))    "thread"
lua_typename(L, lua_type(L, -2))    "thread"
lua_typename(L, lua_type(L, -3))    "thread"
lua_typename(L, lua_type(L, -4))    "nil"
lua_typename(L, lua_type(L, -5))    "nil"
lua_typename(L, lua_type(L, -6))    "nil"

My guess is that the scripts have some tasks running (even if I don't call any script function from C++), maybe some cleanup tasks and this tasks interfere with the normal shutdown.

Any hint about why is this happening and how to solve it?

¹The code is way more complicated, this is just an example.