To verify that it is working, exit configure mode, and do:
$ show ubnt offload IP offload module : loaded IPv4 forwarding: enabled vlan : enabled pppoe : disabled gre : disabled IPv6 forwarding: enabled vlan : enabled pppoe : disabled IPSec offload module: loaded Traffic Analysis : export : enabled dpi : enabled
or, in configure mode, you can do "run show ubnt offload" which does the same thing.
The key is to verify that the IPV4 and IPV6 forwarding show as enabled. And PPPOE and VLANS if you are using them. If they are enabled in the config, but show as NOT enabled after this command, it means that you have accidentally enabled a setting which is incompatible with the offload.