Disconnected agents are deleted prior to the 90-day default in Aria Operations for Logs.
The forget-agent-time-secs parameter has a default value of 7,890,000; therefore, inactive agents age out after approximately 90 days by default. (Manually clean up the list of inactive LI agents in Aria Operations for Logs)
Aria Operations for Logs servers were restarted several days after the agents disconnected.
Aria Operations for Logs 8.18.x
Disconnected agent states are stored in volatile memory. A server reboot clears this memory, removing any agents that have not reconnected. Consequently, it is expected behavior for such agents to be deleted from Aria Operations for Logs.
Start the agent to reconnect it to the Aria Operations for Logs servers.