DoK,
Do you monitor your resting HR? By that I mean do you wake up and immediately take your HR before you sling one foot out of bed? If so, what did you find?
I agree with the lack of warm up/change in routine theory as the most likely culprit thus far.
Having said that I've had great races when my routine was broken and poor results when I did everything else right.
IIRC your racing volume is up as of late, non? Could it be that there are no more cookies in the jar?
As Ex mentioned earlier, your recovery will reveal all.