win 7times, lose 3times, onyx1512 to diamond6
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.