Xi5/Xi6 and User Owned Modem

I’m getting mixed messages on whether or not my router is the issue behind my problems.

I have a Netgear Nighthawk AC1900 modem/router.

I initially had an Xi6 box connected via Ethernet cable. Every time I turned it on, I got the error code XRE-10007. After changing a channel or something, everything worked. The sports app never worked, with error code APPS-04233. On top of that, it had a pretty bad flickering issue, specifically when it came to instant replay during sporting events.

Chat with Xfinity tells me that I’m having these problems because I don’t have a compatible modem.

I go to the store and tell them that I guess I need an Xfi router, but am told no, the wireless boxes are compatible with anything and I probably just got a faulty box. However, they didn’t have any Xi6s and they sent me home with a temporary Xi5.

Set everything up and all of the same errors are still there, however, the flickering is totally gone (so far).

I guess I just want to know what the real answer is. Do I have to return my modem and give more money to comcast to get this wireless box to work properly or is this something else?