This issue has probably nothing to do with the RDS encoder itself.
In order the RDS Spy can rebroadcast at full RDS rate of 11.4 groups per second, entire chain must be synchronized. The RDS encoder confirms transmission of each group, next group can be sent upon this confirmation. If the rebroadcast plugin doesn't receive the confirmation, next group is sent upon timeout event, resulting in smaller group rate.
That means you should verify again
- if you can communicate with the RDS encoder (not only send data but also receive data from the unit)
- if the RDS encoder's speed is equal to the speed set in the rebroadcast plugin (19200 bps)
- if "Bidirectional" communication option is checked in the plugin
- if RDS Spy sends groups at right rate, this can be verified in the rebroadcast plugin like on the picture above