My friends and I recently starting playing Halo 5 Swat again. After playing the 10 matches to be placed in a league i was put in platinum 4. Since we started playing more I have not since moved up a league. Yesterday we won 6 and a row and I my XP bar to Platinum 5 barely moved if at all. Just wondering why this is. I lose a lot of xp on the bar after a loss too.
It’s intentional; it is the new way ranks are handled in Halo 5. Your CSR (rank) will not go up if it is higher than your MMR (true skill). Your MMR is hidden so you don’t know what it is, but if you are only gaining +1 CSR for a win and losing -15 CSR for a loss, it means your CSR is too high and the game isn’t letting it get farther away from your actual skill level.
More info can be found here.