1) What is the output of the gctload -t1 , gctload -t2 , What is the GCT_LIB version ?
2) If (1) is showing not issue , What is the NUM_MSGS configured , maximum allocated ? Congestion counters, if the NUM_MSGS is below 600 , try to increase this to 10000 only for testing
3) If the traffic is sent to your links via a concentrator/MUX , and always the same links get no traffic , check with the concentrator , also I faced similiar problem due to bad BNC quality and poorly fitted inners , but this was always showing BER before stopping or bad impendance matching ,check that from those links using K15 PA
4) If you have no BER errors before the problem , try to change the PCI slot of the card
pls share config.txt and system.txt