I've seen (on 4.4.2) that Ubiquiti MCS (on Elevate) doesn't support MCS above 7. Is it normal?
Are you using a 1x1 radio, like a AirGrid or Bullet?
I'm using AG-HP-5G-XW
Yes, this is normal for this type of the devices, because they can have only one chain/polarisation and don't support 2x2 MIMO.