I have two Xboxes (Xboxen?) here. I did a port forward for each Xbox and the NAT test comes back as open. One is hard wired, an Xbox One X, and it' works fine. The other Xbox is an OG Xbox that uses wireless. Neither Xbox has any problem staying connected while playing games. The OG Xbox on wireless seems to have problems where it is no longer connected to Xbox Live when waking the system from sleep. I'm not sure what's up with that and I haven't spent any time debugging it. A reboot of the Xbox gets it back online.
I have a full stack here, 3x MR42, 3x MS120-8, and 1x MX67. ISP is Google Fiber.