Hopefully someone will be able to offer some advice on a little problem i'm having. I had a back wheel and cassette replaced on my bike and got it back yesterday. I went out for a spin last night and noticed that when i tried to shift to the middle ring at the front it wouldn't shift. When I pressed the paddle again it dropped to the small inner ring and I then had to shift up to the middle ring. Does this sound like a derailleur issue or a calbe tension issue or something completely different? I won't have time to leave it back in to the workshop as I'm doing a sportive on Saturday the 5th July.