$config['sess_cookie_name'] = 'mydomainsession.id';
it's not work
If this is about using 'mydomainsession.id' as a cookie name, then it cannot be regarded as a bug, since that is an accepted value for a cookie name. If you still think this is a CodeIgniter internal bug, please provide more detailed steps for reproducing the problem, but also what exactly isn't working.
However, if you need help with debugging an issue with your own application, you should head to the forums.
Also, this seems addressed on #3108.
Thank you @gxgpet
Most helpful comment
Thank you @gxgpet