This issue happens randomly with a partner Gateway.
After sending (or receiving)  file, the transfer requester CFT does not see the ACK message sent back by Gateway so that the transfer State will remain on "T" and never change to "A".

In the log, there is an error:
CFTT14E _ Transfer Not found <IDTU=00000000 PART=PXFBGWS  IDF=POT      IDT=J2406153 STATE=T/X>

This message means the reply message has been received but the local (CFT) transfer to be acknowledged is not yet in state T ou X.

The reason of the issue is in PeSIT conception: there isn't ACK mechanism defined in PeSit protocol. What is implemented in CFT and Gateway is an acknowledgement in application level. It's a real transfer of message type using a new  (parrallel) network session. So in CFT side, the ack may arrive (randomly) before the end of acknowledged transfer is recorded in catalog with state "T". In this case, the ACK is rejected because in the principe, only a transfer ended (state "T" or "X") can be acknowledged.

When the error happens, if the partner is another CFT, the ACK will be sent again. But if it's Gateway, the only solution is to wait a bit (2-3 seconds in Gateway side). before sending ACK message to CFT.