My concern is related to agents are not showing in agent overview dashboard. Only I can see one database agent. Previously more than 20 DT agents were connected to my environment, suddenly they have gone. Below mention log I am able to see in logs file:
[RepositoryDataWriter] error during writing repository data: The login timeout( 60 seconds) was reached, most likely because repository is not connected (UNABLE_TO_CONNECT)
Also I saw today, PWH was disconnected again I have connected same but still agents are not connected.
PWH disconnection will not impact the situation you are going through.
Do you have a standalone collector or on the AppMon server?
Do you have a firewall between collector and server in case of different zones/vlans?
If you have a standalone server then telnet the port # 6698 http 6699 https from the collector server to your AppMon server whether it is accessible or not.
What is the status of your standalone collector?
Is the database agent was connected to same collector?
Check the collector and server logs to gather some more information.