The following has worked for some users with similar problem:
Try to increase the value of the max_input_vars variable in php.ini. This variable was introduced in PHP version 5.3.9 and has the default value of 1000.
You can read more about it in the PHP documentation:
http://php.net/manual/en/info.configuration.php
max_input_vars 1000 PHP_INI_PERDIR Available since PHP 5.3.9.
How many input variables may be accepted (limit is applied to $_GET,
$_POST and $_COOKIE superglobal separately). Use of this directive
mitigates the possibility of denial of service attacks which use hash
collisions.
You could try to increase it to 1500 or 2000.
Estimate:
Using the data below, we can try to estimate how many POST variables we are sending, given a certain number of menu items, when we press the Save Menu button
It seems to be:
"number of POST variables" = 11 * "number of menu items" + 9
which is equivalent to the line:
y=11x+9
Then we can build the following table:
In your case, we see that if you need to save 100 menu items, you need to send 1109 POST variables, so your max_input_vars must be at least 1109.
Similarly when we add items to the menu (via Ajax POST)
we get
"number of POST variables" = 10 * "number of menu items" + 3
which is the line:
y=10x+3
The corresponding data table is:
When we add 10 menu items, we send 103 POST variables.
Data:
Just to show you the amount of $_POST data when I save my menu with only 5 items:
Array
(
[menu-name] => simple_menu
[save_menu] => Save Menu
[closedpostboxesnonce] => xxxxxxxxxx
[meta-box-order-nonce] => xxxxxxxxxx
[update-nav-menu-nonce] => xxxxxxxxxx
[_wp_http_referer] => /dev/wp-admin/nav-menus.php
[action] => update
[menu] => 58
[menu-item-title] => Array
(
[1135] => home
[1131] => page1
[1130] => page2
[1132] => page3
[1133] => page4
)
[menu-item-attr-title] => Array
(
[1135] =>
[1131] =>
[1130] =>
[1132] =>
[1133] =>
)
[menu-item-classes] => Array
(
[1135] =>
[1131] =>
[1130] =>
[1132] =>
[1133] =>
)
[menu-item-xfn] => Array
(
[1135] =>
[1131] =>
[1130] =>
[1132] =>
[1133] =>
)
[menu-item-description] => Array
(
[1135] =>
[1131] =>
[1130] =>
[1132] =>
[1133] =>
)
[menu-item-db-id] => Array
(
[1135] => 1135
[1131] => 1131
[1130] => 1130
[1132] => 1132
[1133] => 1133
)
[menu-item-object-id] => Array
(
[1135] => 477
[1131] => 1020
[1130] => 1028
[1132] => 791
[1133] => 603
)
[menu-item-object] => Array
(
[1135] => page
[1131] => page
[1130] => page
[1132] => page
[1133] => page
)
[menu-item-parent-id] => Array
(
[1135] => 0
[1131] => 0
[1130] => 1131
[1132] => 1131
[1133] => 0
)
[menu-item-position] => Array
(
[1135] => 1
[1131] => 2
[1130] => 3
[1132] => 4
[1133] => 5
)
[menu-item-type] => Array
(
[1135] => post_type
[1131] => post_type
[1130] => post_type
[1132] => post_type
[1133] => post_type
)
[menu-locations] => Array
(
[primary] => 0
)
)
When I add 3 items to them menu, the POST data is:
Array
(
[action] => add-menu-item
[menu] => 58
[menu-settings-column-nonce] => xxxxxxxxxx
[menu-item] => Array
(
[-56] => Array
(
[menu-item-object-id] => 1728
[menu-item-db-id] => 0
[menu-item-object] => page
[menu-item-parent-id] => 0
[menu-item-type] => post_type
[menu-item-title] => Page 1
[menu-item-url] => http://example.com/page1/
[menu-item-target] =>
[menu-item-classes] =>
[menu-item-xfn] =>
)
[-57] => Array
(
[menu-item-object-id] => 1724
[menu-item-db-id] => 0
[menu-item-object] => page
[menu-item-parent-id] => 0
[menu-item-type] => post_type
[menu-item-title] => Page 3
[menu-item-url] => http://example.com/page2/
[menu-item-target] =>
[menu-item-classes] =>
[menu-item-xfn] =>
)
[-59] => Array
(
[menu-item-object-id] => 1658
[menu-item-db-id] => 0
[menu-item-object] => page
[menu-item-parent-id] => 0
[menu-item-type] => post_type
[menu-item-title] => Page 3
[menu-item-url] => http://example.com/page3/
[menu-item-target] =>
[menu-item-classes] =>
[menu-item-xfn] =>
)
)
)