if you are able to access your router at home. Select the device you are needing to do multiplayer on (that isnt working) and open port 4555 (UDP). I thought doing the computers time setting fixed it (but it stopped working next time i played) but once i opened that port for my laptop, it works fine (except the xbox connectivity app setting (or whatever its called) says it isnt working anymore (despite the fact that it does and it works even better. Before i could only see cross-platform games (and trying to connect wouldnt work) but now it also shows LAN games and cross platform games (with friends) and they connect.
Hopefully that helps some people but if you dont have access to your router settings you wouldnt be able to change that.
On a side note that router setting was in the firewall section of the router.