Monitors reports to be down

Sometimes, when I have lost my network connection, or just seem to have been away for some time, my monitors never goes online again. They are constantly "red" and reports 0 uptime the last 24 hours.

So I try to restart appmanager, I can even press "fetch values now" and it works fine. But I still have a 0 seconds uptime and the monitor is Red.

This is solved by trying to add a new monitor, the same again (overwriting the old one). Now it says that the monitor were added fine - but all it did was kicking the existing monitors and it now starts to display "green" values again - so it works.

How can the monitors go dead without waking up again? Any special suggestions? This is mainly for BEA Weblogic 8.1 monitors + JMX monitors.