Custom list - Item level permissions

Hi,

I have a site with a custom list

(1) The custom list has 800 items

(2) Each item has item level permissions and is shared with the appropriate people

(3) A custom permissions "EditOnly" is created to prevent deletion of items

I have a limited number of users with the "EditOnly" permissions that cannot edit the item. The majority of the users can, but some exceptions cannot. And they all have the same permissions "EditOnly". Any ideas ?

Can the 50 000 item permissions limitation play a role in this ? I have created a new item and stopped inheriting permissions. This worked, so not yet at 50 000. Any idea how to count this number ? The items multiplied by the people that have some level of access ? And the groups count for one of do I need to expand the group to the users ?

Thank you,

Marc