I have a site with a large number of nested menus.
I solved the problem after following the solution proposed here
and including max_input_vars setting.
For some time this worked but now when I attempt to save menus I get
Service Temporarily Unavailable The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.
and the logs report nothing.
I try to increase to max_input_vars setting to 20000 but to no avail.
Any help would be invaluable.