After upgrade RB1100AHx2 from 6.20 to 6.21.1 I lose all of my LAN connections. All WAN was work properly.
I downgrade to 6.20 - OK. Please test your firmware before release.
This firmware also killed my Miktorik RB1100x2AH ( The problem solved by downgrade. Also in the low-end models have to be a problem with IPSec (I mean RB750G).