Nethserver public IP Address Gets Empty

NethServer Version: NethServer release 7.6.1810 (final)
Module: 3.10.0-957.12.2.el7.x86_64

Hi. Two of our nethservers is having problem with the external public ip. Once in a while it cannot get a public ip. What do you think is the problem? send helppp


How are nethservers connected to the Internet? What type of line is it?