Ah, Navigraph doesn't have our flightplan format, which is weird, cause they have it on Simbrief. I guess you'll need to contact them to add our fpl format to the Navigraph website - or alternatively, just download the fpl file from simbrief
That sounds weird, it should work just fine.
Could you please try to delete your iniManager folders in AppData/Local and AppData/Roaming, then reinstall and see if the issue persists?