Hi,
ok, so this is limited to the x440. You should validate you are not exceeding some hardware limits of the x440 here. IP Multicast, ARP...
I don't know if the Multicast table could be (part of) the issue. But this is something you need to address anyway.
When you reboot the x440, you reset every forwarding tables. Over time the x440 only are experiencing issues. I'll start to look at some resources exhaustion.
Have you opened a case with our GTAC on that matter? They should be able to drive you into this troubleshooting.
Best Regards,
Stephane