lost connection and a bug

Hi,
Yesterday I played 6-7 hours and encountered two issues. The game is good but the issues are frustrated. Especially the last hour was a nightmare.

Coop
1, Mission 4, there was a chance that the role died below the surface and then I lost connection.
After that, when I join back, I cannot select a role but my teammates can. When they select and start the game for a few seconds, all of us will return to role selection interface, again and again.

2, I kept losing connection when I was having a coop with friends. Everyone is good except me. Join fireteam, play, lose connection, rejoin fireteam, wait, exit fireteam, rejoin, play, lose connection …

My network is cool, 500Mbps fiber, Singtel, all games are good except Halo 5 Coop, and only Coop I will suffer the connection issue.

I am NXOE member.

I am dying! Please suggest!