could not find a server that was suitable for all members of your fireteam
i
need
help
with
this
Not sure about custom games but I believe the online server issues is a known issue. Not sure if there’s going to be a fix anytime soon.
All I can suggest is go to the Halo support page, submit a ticket. (not to be confused with the Halo support forum page)
Though I have posted about the servers and they said “Thank you very much for your submission. Halo Support is reviewing the information provided and will provide an update shortly.” 3 days ago so I’m not sure what 343i are doing about the server issues.