After 4-5 hours Openfire becomes slow

Team - I have setup openfire server 4.0 in a high configured Linux box. I open 2 SPARK applications in 2 PC in LAN and start chatting in a Group/Conference.

At initial 2-3 hours messages go to other users Spark within 1 seconds …it goes soon after I press enter… But when time goes response time gets slower.

After 3-4 hours server online it takes over 6-8 seconds for the message to appear in other Spark windows.

But if I restart Openfire server then it again becomes very fast.

Can you please tell me what could be the issue. I have tried installing in few more dedicated servers but all same. I have almost 95% free java memory and 0% CPU usage.

Can you please tell me how to find root cause.

Thank you