rrd history chart disappears under conn, memory and disk after 24 hours

Hi,

I installed and configured xymon-4.3.0-beta2. Everything looks fine. But there is one strange thing beyond my understood. The rrd history chart disappears under tests/columns of conn, disk and memory after running 24 hours. But I can see these charts under column trends. No time effect to the tests/columns of cpu and my custom tests. These rrd charts will stay there as far as time goes.

If I add a new client, I can see these rrd charts under conn, disk and memory during the first 24 hours (or the first day).

Anyone sees the same phenomenon? Did I miss something in configuration?

Thank you in advance.

-- Zhongyu Chen