Recipes+ causes the anti-gravity device not to work correctly. Fall damage is prevented, and flying in creative emits the right sound, same as switching to Spectator. But liftoff is impossible. Same in single as in multiplayer. A friend of mine could fly on the same server I couldn't, the only difference was I had recipes+ installed, whilst he hadn't. (The server hadn't too, but since singleplayer didn't work either, I don't think that is the issue). For reference, here is a list of the mods used (excluding Recipes+):

I find this very weird and have no idea as to the cause of the problem