Best advice I can offer is to stop using the old DHCP configuration under "system services dhcp" and start using "set access address-assignment...".
I'm not sure if you can do that under 11.4 so if not, upgrade to 12.1 if you can and then use the new "access" dhcp configuration. I've had a lot of problems with the old method on my SRX220 that you're having on your 210, and I've heard others having the same issues as well. Configuration example would look something like this:
user@host> show configuration access
address-assignment {
pool wired {
family inet {
network 192.168.100.0/24;
range wired {
low 192.168.100.2;
high 192.168.100.254;
}
dhcp-attributes {
name-server {
8.8.8.8; or your ISP's DNS server
}
router {
192.168.100.1;
}
}
host PC-1 {
hardware-address 08:60:6e:67:ec:aa;
ip-address 192.168.100.2;
}
host PC-2 {
hardware-address c4:4e:ac:03:4e:ed;
ip-address 192.168.100.3;
}
}
}
user@host> show configuration system services
dhcp-local-server {
group wired {
interface vlan.100; logical or physical interface participating in dhcp
The bindings are configured where you see "host PC-1" and "host PC-2". I've found this method much more stable/reliable. Your ip scheme and participating interface will be different as this is just an example.