Thank you for posting this Keilly!
A bug fix is desperately needed for this issue. I can confirm I'm having the exact same problem with the firmware listed above. I thought my router had died when my WAN access was killed the other day. I cycled my router on and off several times along with my cable modem. I called Brighthouse to confirm it wasn't an issue with my ISP. I reset the router back to factory defaults to no avail. I never would have guessed that NAT port forwarding for my Xbox Live gaming was the root cause of the issue.
I had to enable Parental Controls and then disable them again to get the router fully functioning, even after the reset to factory defaults. I wouldn't have known how to get the router working again had I not found another T-Mobile support thread. I was very close to calling T-Mobile and requesting a new router. Good thing I didn't or I would've had the exact same issue with the new router. To prevent the issue from cropping up again (until we get a patch to fix the problem, fingers crossed), I had to resort to putting my Xbox One in DMZ and am no longer using the port forward feature.
Please patch the firmware!