Have you changed up your schedule at all? I find that I pace a solid 30 seconds/mile slower (running) the day after a solid bike ride, for the same amount of perceived effort. I figure I'm getting just as good a workout and settle for the increased time. I have taken significant time off my half marathon PR this summer following this strategy, so I assume it's decent enough.

Another thing I can think of would be to try switching around your run workout for some variety. Do you always run a steady state, or do you try hills, tempos, etc to change things up?

And you seem to be doing a lot; it is always good to take a recovery week once a month or so. (I try to do 70-80% of the previous week's mileage.) Maybe you just need a break to get your legs feeling good again?