There is a bug report for ELO and arena points for team/cooperative games
https://boardgamearena.com/bug?id=11297
https://boardgamearena.com/bug?id=11297
When you play team games (e.g. Belote), BGA considers that you did tie with your partner. So, more you're partner have a low ELO ranking, more your own ELO ranking will degrade (whatever you win or lose).
However, it should be considered as more difficult to win with a lower ranked partner, so your ELO should grow (or at least not being affected by your partner ranking).
Can we have a response from the admin team ?At the moment, you get punished if you play with lower elo players, instead of rewarded.