After buying a new hive, restarting the game and clearing caches, my hive started working as normal again. I had got it up to perfect before it started diving - so just a glitch I guess, but it wasn't just the one hive. I don't know where it stems from, but it's fixed for now. I'm up to the same amount of time again (about 2 weeks) so we'll see. I also like smoke, harvest, clean, feed. I think so long as you clean and feed them every 12 hours they'll continue to produce perfect honey.