I have v5, so that shouldn't be an issue for me, right? Judging by yours and @eduperez's comments, it seems as though it is very unusual for me to be experiencing this problem, and the cause is likely to be the way I have other things configured...although I don't see how. I haven't changed much manually from the default, freshly-flashed firmware besides interface names, a few firewall settings and adding a few simple software packages.
Do you mean connect my old router's WAN port to an available port on the C7? Sorry but my Networking 101 course from 2012 is failing me here (or rather my memory of its content). But the rest of your post seems to suggest such a network design, if I do remember things correctly. Just wanted to make sure 