TCIP error Default Gateway

Error by TCIP – Resetting erroneous Default Gateway at laptop shutdown:  I have 3 Dell Inspiron Laptops with both Ethernet and WIFI capability.  I use them at both my home and my office. 

My office has a Comcast Business Class modem.  My home has an Xfinity SMC modem (model SMCD3GNV).  When at home connected to either Ethernet or WIFI the TCIP addressing works correctly.  All there machines are set to automatic DHCP addressing. 

At the office, whether Ethernet or WIFI connected, the Default Gateway is set to 192.168.21.220.  The required Default Gateway = 192.168.21.1.  Therefore they will connect to the Comcast Business modem but will not open any WEB pages.  To get access to WEB pages on all three machines I have to do one of the following: (1) Uninstall the Network devices and then scan to reinstall them.  That resets the Default Gateway to the required 192.168.21.1 o (2) use CMD to release and renew the IP address.  That resets to the correct Default Gateway or (3) Reconfigure the TCIP settings to fix the Default Gateway to 192.168.21.1.  If I do that then the computers cannot be used to access a WEB page if not connected to the office modem.  I would then have to reset the TCIP addressing back to automatic.  I have several desktop Dell computers in my office which do not have this problem behavior.  Only the laptops reset to the 192.168.21.220 Default Gateway when shut down. 

I have spent several hours with Comcast advanced tech support and with Dell Advanced tech support, but neither can explain what causes the resetting or how to truly fix it. 

One of the 3 Dell Insipiron laptops is just newly delivered and fresh out of the box with the initial Windows setup.  No software added or and changes in settings. It behaves this way right from the Dell factory.

Can anyone tell me what causes the behavior and how to actually fix it other than manual work around?