Doing a little rethink...the lowered HR is probably your best indicator. That's a chronic or acute fatigue indicator, or evidence of a lack of warmup.
Unless you had a full or partially full stomach from eating too much too close to the race, I'd pull feeding off the list. Meltdown came too early in the race.
I end up doing a lot of early morning races, I make it a point to get up three hours ahead to eat and just wake up. And I find that the further I am along in my peak, it takes harder warmups to have me ready to go; my resting HR gets pretty stoopid.
Be interested to hear how this week's training/recovery rides go.