To quote the book (Mindfulness in Plain English) that was earlier recommended in this thread and in the article:
"Meditation is not some mindless formula which gives automatic and predictable results. You can never really predict exactly what will come up in any particular session. It is an investigation and experiment and an adventure every time. In fact, this is so true that when you do reach a feeling of predictability and sameness in your practice, you use that as an indicator. It means that you have gotten off the track somewhere and you are headed for stagnation."
I can't really know if this is the reason why you felt like you had hit a rut - Just had to leave this comment for your consideration :)
"Meditation is not some mindless formula which gives automatic and predictable results. You can never really predict exactly what will come up in any particular session. It is an investigation and experiment and an adventure every time. In fact, this is so true that when you do reach a feeling of predictability and sameness in your practice, you use that as an indicator. It means that you have gotten off the track somewhere and you are headed for stagnation."
I can't really know if this is the reason why you felt like you had hit a rut - Just had to leave this comment for your consideration :)