System breaks every thursday night

[ddtesting]

Hi,
I'm debugging an interesting issue that I haven't had on previous OPNsense installations.  Every Thursday night the internet connection goes down, I can still access internal connections such as the OPNsense router itself.  The router is fed from a WOW cable modem/router so the gateway for the OPNsense router is a private IP (192.168.0.1).  I did not block bogon networks or private IPs.  I have upgraded the system to the latest version 18.7.9.  When I restart the system on Thursday, everything returns to normal operation.  I tried looking at the logs but haven't quite figured out what is going wrong.  On the days that the system is broken there are some error messages such as "Starting alarm pinger, apinger" "apinger: no useable targets found"
I also attached some errors in an attachment. 

Any thoughts are appreciated.  Thanks