As per this KB whenever the SNMP ISIS interface adjacency status is polled it would show information for all interfaces & kept varying time to time.

Basically its not a buggy behaviour its expected design issue when you have configuration as below also Need to check below points , 

1. Loopback interface is seen in the MIB OID output because loopback interface is called in the isis Protocol even though its not a physical port & logical interface which is expected.
2. because of this particular configuration where all interfaces are called inside ISIS protocol for PUNE device while poling data also all interfaces stats will be polled unlike the other routers.

    interface all {

      ldp-synchronization;

    }

Resolution: After removing "set protocols isis interface all " and adding it in particular to those interfaces only which is having isis neighbhorship command SNMP stopped polling ISIS info for all interfaces as expected and only expected ones were captured.