Hi,
i tried to order the group field into my custom post type backend but when i reload the page the order not work.
I also tried to disable all plugin and not works.
Thank you for the patience, I had a look at this for you in a bit of detail.
The problem here is that i'm unable to identify the cause of the issue, in particular i've tested creating the custom fields with Advanced custom fields and disabled all the plugins including Toolset and the issue still remains where i'm unable to re-arrange the custom fields.
At this point there isn't much that I can do as the issue could be unique to your site. In a fresh copy of wordpress the issue doesn't occur and i'm able to re-arrange the custom fields without any issues. Perhaps you can open a ticket with the wordpress core support to see if they are able to assist you with this one. https://wordpress.org/support/forums/
They might be able to shed more light on this one for you as the issue here is out of our support scope given that it is wordpress core feature.