Serial COM lost

I used the ConfigTool for a WIZ108SR successfully.
The purpose was to connect the module to a Modbus serial server.
And that is working.

Sometimes, when I re-connect my laptop, the TCP/IP side seems to still work but the serial side sends only time-outs…

I can solve this by opening the configTool and by just clicking on SETTING icon.!!

Any idea?
Pierre