What is the NSM version?
You will need to collect the Threatanalyzer.log file from the client system/server you are using to browse the RTTA.
The TA log can be located on your <user folder>\mcafee\networksecuritymanager\<server IP or name>\threatanalyzer folder.
Thanks. That is quite an old version.
Looking at the 188.8.131.52 release notes I can see the follwoing defect being fixed:
569584 In the Threat Analyzer, acknowledged alerts are displayed after a re-launch.
You may want to upgrade your manager to see if it resolves the problem.
I would advise to check the release notes fot the 6.x version to get the correct upgrade path and try upgrading to the latest 184.108.40.206 NSM build.