I have noticed over the last 2 years or so that as we have replaced the 1100Ahx2 routers with the 1100AHx4 the x4's seem to have an issue where they partially lockup. It seems to still route whatever was connected to it when the lockup occurs but it does not respond to any management connection or new connection until the router is either rebooted or replaced. Has anyone else seen any odd behavior out of this model? I have made tickets about the issue but it seems to be related to this model only as the older x2 routers do not have the same problem and better CCR routers do not have the issue.

You might set the cpu frequency to a lower rate in
/system routerboard settings

The later 6.47 series fixes the issue with them. 6.47.7-6.47.10 are the versions you'll want to run. The earlier versions has some snmp issues that would do exactly as you describe. I have around 50 of them in the field and experienced what you're going through. My preference is 6.47.10