Netgear Nighthawk R8000 X6 AC3200 2.4GH wifi drop out problem

I am using this router behind the Primary ISP's router for a VPN router.  I live in Mexico and if I want to watch U.S. only content I need the VPN.

Because I use it for this purpose it had to be reflashed to DD WRT.  The build on that is pretty new, like January of this year.

I have this thought this problem may be caused by a conflict between the two routers.  They are pretty close together, very difficult to separate them by much.

If anyone here is familiar with DD WRT are there settings on the 2.4 channel in DD WRT I might change to minimize conflict?  

5GH works fine but doesn't carry far in a large house with concrete wall construction.