Inactive replication slots

Hello Everyone,

I have a primary Postgres server with 2 standbys setup using streaming replication. Both the stand by servers are using
thereplication slots. 
Today, when I checked the status of replication slots on primary, they are showing active= ‘f’. The data is replicating
withno issues but when the slots are inactive I know that the wal files generated after the restart_lsn will not be
deletedand retains the transactions, which is very critical. 
I am not sure exactly why the slots are inactive and if there is a way to activate them back?
I tried restarting both primary and standby but sis not have any effect.

Thanks and Regards,
J. Teja Sri.