If you notice an issue regarding the performance data collection for the Linux monitor with RHEL 8 & above (No data in GUI) then from the Applications Manager GUI --> Admin --> Product Settings --> Logging --> choose Print all logs option and save setting.
Check if the below log trace is observed in the AppManager/logs/nsm/nmsout.txt file.
-Install package 'redhat-lsb-core' to provide command 'lsb_release'? [N/y] ----
During every polling the Applications Manager executes the commands to fetch the data from the remote server by establishing an CLI based SSH session, when it executes the command if we are getting an response from the server like above this will interrupt the data collector threads hence resulting in data collection failure
Solution:
yum install redhat-lsb-core