You will find below Error message from Agent logs
20200721/140102.842 - U02002040 Disconnected from '*IPC(LISTENER)' (socket handle = 's=30,ID=257').
20200721/140138.058 - U02000257 Upload of file '/usr/local/uc4/agent/bin/../out/OAPEQQXD.TXT' completed successfully.
20200721/140219.442 - U02000257 Upload of file '/usr/local/uc4/agent/bin/../out/OAPEQQXD.TXT' completed successfully.
20200721/140219.443 - U02003073 Agent Prozess 'AGENT,PID=10792' shutdown has been initiated.
20200721/140219.444 - U00029002 Report '180359379' ended abnormally.
Release : 12.3
Component : AUTOMATION ENGINE
Shutdown on Agent was initiated Manually by any user.( Agent didn't loose its connectivity Automatically).
User Must have shutdown the Agent, unknowingly or knowingly.
You can check service manager logs during the issue occurrence time for User details, who has initiated the shutdown on Agent.