After reading around, i’ve been able to edit the php.ini and increase max_input_vars from 1000 to 2000 which has fixed it. My menu is currently 192 items long so I’m guessing it may need to be increased a little more if the menu expands any further!
I don’t think this is specific to the plugin as I have now deactivated the plugin and still have the same fault. Please could this be deleted as I will re-post in the correct area?