Having flashed the latest v16 nightly everything seems good apart from speaker & mic when making or receiving calls. (No sound either in or out)
Of the three possible reasons I've found the first two do not fix it, these being generic problems with google voice settings and a bug in build.prop within the system folder. I also read somewhere that it may be down to which stock ROM was being used previously (G900FDXXS1CQD1_G900FDOXE1CQA4_G900FDXXU1CQA4_HOME .tar) which was the latest 6.01 Russian build as the handset was Russian in origin.
If anyone has a SM-G900FD running v16 working in calls I would appreciate you posting the firmware build you were previously running or any other suggestions.