I am having problems with SharePoint custom list. Everything was fine until they asked me to add a new item in the list. Now a specific user can't edit any of the items in the list since the edit button was disabled. He belongs to the same group but the issue where the edit button was disabled is limited to him only.
It seems some cache kind of issue. Just ask him to try from other machine or restart the browser. Or just give me permission directly to check if he can edit than. And what kind of new item you added? Try deleting that new item and then check if nothing works.