Changing the default form url removes permissions

Question

I want to change the default forms for lists with CSOM C#, which is already working fine:

using (var ctx = new ClientContext(url))
{
    ctx.Credentials = new SharePointOnlineCredentials(Username, Password);

    List spList = ctx.Web.Lists.GetByTitle(list);
    ctx.Load(spList);
    ctx.ExecuteQuery();

    spList.DefaultEditFormUrl = "_forms/EditForm2.aspx";

    var group = ctx.Web.AssociatedOwnerGroup;
    ctx.Load(group);
    ctx.ExecuteQuery();

    spList.AddPermissionLevelToGroup(group.Title, RoleType.Administrator);
}

However, even if I add permissions to the owner group, I can't manage to access the edit form after setting the new one this way

Answer 1

I found out what was the issue, it's not that permissions were removed from setting the URL, but that my user did not have permissions to access _forms/EditForm2.aspx.

If the file is instead located in Lists/list2/EditForm2.aspx, everything works just fine.