Maybe, and I don't use that maybe lightly. There could be a short lease on your DHCP addressing, and the ip address changes and you no longer have a valid address? Maybe try a cronjob
0-59 * * * * [maybe your user account] ifconfig -a >> $HOME/my_ip.txt
I say maybe on the user account part because when I did it that way on a system, it didn't work for me, even though some pictures on google when typing cronjob said to. Also I'm only kinda sure putting a dash works, as I haven't tried it. Another option is 0,15,30,45 as replacing the 0-59 argument. This will be less to look through, although all you will need is the tail of the file to see if this might be the problem.