Sometime Freepbx distro don't register to client

Dear All,
Now I use Freepbx Distro version 10.13.66bit with Asterisk 11. I have a problem. every day, 1 or 2 times : IP-Phone don’t register with Freepbx with randomly. When I restart Asterisk with command line " service asterisk restart". IP_Phone register with FreePBX normally. " Anyone have any ideas? Thanks in advance!!