Mythic Firefight matchmaking is down.

Games Halo 5: Guardians
1

Attempting to join a Mythic Firefight match continuously results in “Matchmaking encountered difficulties.”

EDIT: Now it’s failing to join all matches, except custom games.

2

I’m having the same problem

3

Seems to be the same issue as yesterday. Took approximately 6 hours to fix.

4

Try restarting your internet router. It generally takes around 5 minutes, but will flush out the stubborn problems out.

5

At the time you posted there was an Xbox Live outage that has been affecting people over the weekend. It should be cleared up now but I would keep an eye on the Xbox Live status page just in case. There is also a large thread in the Halo 5 forums that any discussion / updates can be directed to.