One way Reflector to Repeater YSF audio.

[GW4OBA]

We have an XLX reflector which transcodes D-Star and C4FM, this is RF linked to our FM/C4FM VHF repeater.
The link is provided for by a repeater builder board running the latest version of pi-star connected to an FTM300 radio which provides the RF link to the repeater, and the data connection to the reflector.
When a station accesses the repeater in C4FM mode a contact can take place between two stations on the repeater. The audio is also captured by the link radio which feeds the audio through the reflector and stations listening to the reflector will receive the audio.
However if the station on the reflector tries to contact the stations on the repeater this is not possible, it seems the audio can pass one way but not the other.
The reflector dashboard does in fact record the two stations communication on the repeater so clearly that data apparently is being transferred correctly, and the station on the reflector is recorded as well so this is a bit of a mystery. The only thing we can think of is a timing issue?
Any help or guidance would be appreciated.
73 Roger GW4OBA