If you were confused by your Navy rank suddenly and seemingly doubling after the Odyssey update, it seems it's a visual/server/API doubling bug, but it doesn't really affect your actual rank in the navy for all other purposes.
Today I tried some more Empire missions and finally received a Navy mission follow-up, taking me to "Marquis" from "Earl", but in fact around Knight or Lord (Marquis is ~2x the Knight in whatever units they use for rank).
So rest assured, at least now, you can still advance your rank, even if it looks doubled and bugged in-game or elsewhere. Just roughly divide it by two…
Yet, the bug isn't nice, it messes up the game and API including Inara and EDSM, but at least it seems to be visual/API only, without any effect on your actual progression or rank grind (or sadly, since I was really looking forward to getting my 'Vette without all the Fed grind!). At least I still got the Navy rank advance missions and proper rank advance (even if doubled visually) when I got to 100% in my real rank, no matter what the game or API showed… It's just now hard to gauge when you get the rank advance navy mission.