HI Robert,
Have you increased any of the default EM clamps (max # of live metrics or # of agents)? MOM and collectors?
There is a chance that you just need to increase memory allocated to Webview in the Webview lax
There are just too many possibilities.
My suggestion would be to start by looking at this kb, it covers most of the common EM performance issues
Introscope Enterprise Manager Troubleshooting and - CA Knowledge
Section A - it covers the known errors, check if you find any of them in your logs and make the necessary adjustment, but very important increasing the clamps will have an impact in the cluster
Section B - it covers a checklist of common configuration issues we found on customer check each of them please.
And very important, if you are using 10.7, I would suggest to upgrade to the most stable build you can contact support.
APM 10.7.0 Hotfixes - CA Knowledge
Now if you are using a pre-10.7 (10.5.x), it is even more critical as not all latest hotfixes are available in support.ca.com, so contact support, if you cannot upgrade to 10.7 contact support to obtain a copy of the most stable build.
I hope this helps,
Sergio