Every time I load up halo 5 now it says “attention cant connect to halo 5 lobby services” I just downloaded this as I’m going through all the campaigns on legendary from the MCC and now I’m on halo 5 I wanted to do it with my mates, however that’s proven to be impossible as they can all connect but I can’t, have tried every single troubleshoot method there is? You name it I’ve done it… can’t think of what to do? I’m praying someone from 343 will see this! 
never had this problem on launch but after I faded away from the game and have no come back it’s saying this. Any help would be appreciated 
Double-check your XBox Live Membership expiration status. It will not connect to Multiplayer Lobby Service if expired. Campaign is locally played.
The following is from another forum’s post.
Guys!!! i fixed my problem!!! the problem was my internet router blocking the game somehow… I just told my internet guy what was the problem and he knew what to do… turned off ipv6…
King Malimik
https://www.halowaypoint.com/en-us/forums/6e35355aecdf4fd0acdaee3cc4156fd4/topics/can’t-connect-to-“lobby-services”-343-please-help/ed51d8ae-882a-43a2-b33a-2bdb0f11ca4c/posts
…same resolution as above from another forum post:
Guys, I found out, what caused the problem. Due to the fact, that IPv4 won’t be supported for too long, from now, internet companies are updating your Modem to IPv6. Just give your Provider a call and kindly ask them to switch back to IPv4. Took him about 4clicks…Quite ridiculous, that some XBox services aren’t compatible with current IP systems…Hope it worked for you guys, for me it did!
U EatYellowSnow
https://www.halowaypoint.com/en-us/forums/e0d9938206f04a598ce84f2c8cadce02/topics/can-t-connect-to-halo-5-guardians-lobby-service/ad195595-b5dd-4c78-b2d1-af4d4d2059aa/posts
hope this helps
Regards