Callpoint callback's are exists but showing: db error: application communication failure

I registered a callpoint for one of the snmp stats table, but the get_elem() callback function status is coming as below: (confd --check-callbacks o/p)

/<MIB-name>/Table/StatsEntry[index='index'][diskName='diskName']/ops - exists()... ***: db error: application timeout
/<MIB-name>/Table/StatsEntry[index='index'][diskName='diskName']/ops - get_elem()... ***: db error: application communication failure

And whenever callbacks are in this states, snmpwalk is failing, in between, with the timeout error as mentioned below:
Timeout: No Response from

This failure I am seeing intermittently, thus not able to figure out the root cause for this.
And one weird behavior I saw, once after restarting the services the callbacks start working as expected and thus snmpwalk also.

Please share your insights on this topic.

almost always means there is some problem with external app that implements a callbacks…
This could be - app not running/callback not registered, crash, timeout, incorrect data provider “protocol usage” (mismatched value types/return code/other), etc.

Make sure you have developer log level enabled with trace in ConfD, and see if devel.log contains more info/problems reported for callbacks being run…