problem installing AX4 (RAX40). Cannot get to internet

Here is my setup before I touched it today. Comcast internet 300 MBS to Arris SB8200 Modem and then to R6300v2. Everything is great.

To "improve" things I did a straight swap of the R6300v2 with the RAX40. After resetting both and unplugging and replugging in the recommended order and then in the opposite order just in case, I cannot get to the internet. Either by wifi or ethernet.

I have swapped them back and forth several times and continue to have great network and internet with the R6300v2 and only local network (with wifi) with the RAX40.

I did a hard reset (with paperclip) on both the modem and also with the router but it did not help. I then swapped the R6300v2 back in and everything works great. Then I also plugged the ethernet cable straight from the modem to the computer without any router and the internet works great. In fact, that is how I am able to post this.

Any suggestions?  (One time I did a hard reset of the modem and was able to address the modem directly 192.168.100.1 through the RAX40 but could not get past this to the internet.)