DNS Suffix hsd1.dc.comcast.net

Hello, asking thru my personal account but I've got several VPN users with Comcast (Xfinity) that keep recieving the DNS Suffix of hsd1.dc.comcast.net on their LAN connection.  With that suffix as a third one added to their searchlist, while on VPN, they lose connectivity often throughout the day.

I remove the DNS suffix from their LAN card but it shows up again the next.

Question is - how do I keep my customers from getting the DNS Suffix of hsd1.dc.comcast.net added automatically by your home routers to their laptops?

Thanks

Ken