j_laing8ti4,
Welcome to the Furuno USA Forum! We are glad to have you :jump
It's very possible it is nothing more than a setting in the NMEA2000 port of the MFD12. Turn your entire system on (GPS, radar, sounder, MFD8, FI504's, etc...)and, then just go to the following on your MFD12:
Menu
Scroll down to System
Chose the General tab
Chose Installation Wizard
From there, let the MFD12 find all the other equipment. Once it has done this, chose the "next" box. Click on the NMEA2000port tab and turn on PGN # 128275 (Distance Log). Click save and exit.
From there your MFD12 will automatcially reboot and your FI504's should see the triplog sentence information. I have attached two pictures of the menus you will see. Please let us know if you need anything else.
Stickman