Items not appearing in menu

[mj0y]

Hello,

I've noticed that a few sub-pages are not appearing in my menu. It should look like this:

1. page
   1.1 page
   1.1.1 page
   1.1.2 page
   1.1.3 page
   1.1.4 page
   1.2 page
   1.3 page

However, in the sub-sub-pages, only 2 items are appearing out of 6.

I believe that the issue is in the plugin, as the menu appears just fine when not using the plugin.
I've also increased max_input_vars in the PHP configuration, however that didn't help.

Please advise.