First make sure you haven't entered a non-zero 'Timing Offset' under Synchronization in Preferences > Audio Sync and Caching (not to be confused with the Manual Offset for record latency compensation). If you haven't, that setting can actually be used to address the issue if necessary, but it's not ideal because the offset that corrects the timing on recording will work against you on playback if you ever use hardware synths. If you only use soft synths, it might be a viable workaround.
But I would first try changing MIDI interfaces. If you use the Fantom's USB, and the RME has MIDI DIN ports, try that, or vice versa. You might also try connecting a USB interface into a different port on the PC.
I have never figured out why some hardware/interface configurations do this, and I don't recall anyone ever completely resolving it without changing hardware.
Maybe some day I'll be able to get my hands on a system that does this, and figure it out once and for all, but I think every suggestion I've ever made has proven fruitless, and none of the 'victims' has ever come back with a definitive conclusion that some particular piece of hardware or config setting was responsible.