When logged in to the Central Manager, you may see some of the sensors reporting a Temporary Communication message.
Go through these steps to fix this issue. You will need to connect to the CMC/sensor(s) via ssh as root to run these commands.
On the sensor:
scm solera_acl update_group 8
scm solera_acl reset_api_aco
scm cmc_exporter real_push -v
redis-cli -p 6378 flushall
On the CMC:
redis-cli -p 6378 flushall
Now refresh the CMC UI page and wait a few minutes to see if the sensor will now show as connected.