I have the same or similar problem,
loosing registration after first register, next registration are lost and registration expires.
i'm registering only 1 line.
i'm not behind router.
i have try versnio 4.14 and beta 4.15 result is the same.
how do i set timer to reregister?
where is registration timing sttings? or it is hard coded ?
how do i improve this situation?