Network gets hang in each 24 hours

Dear Team,

As we have installed 2 501E in HA Mode , I am facing the problem that 

1. We have connected internal web and dns server with the firewall 

2. Every day, The network gets stuck in 24 hours and After stuck when we restart the dns and web server , Again it starts working fine.

3. After restart of server, It works fine for again 24 hours . Previously , It was working fine with 900 D , When it was in standalone.

Can any one please advice me what could be the issue in network