SystemEDGE is a single threaded application, and it will not be able to respond to bulk SNMP requests while it is in the process of updating the MIB.
The following entry in the Sysedge.log is a good indicator the Server is overloaded (CPU and\or disk subsystem) and this is impacting SystemEDGE's ability to refresh the MIB in a timely manner:
query_monitor_entries(): Performance problem detected (monitoring cycle). Elapsed time 185.826648s). SystemEDGE may not be responding to SNMP queries during that time.