Read Thread: Fitbit Data No Longer Syncing
I'm not sure how you normally sync your Fitbit or what has changed for that not to happen automatically anymore, but once you get that working, it should all work fine again.
I don't know what changed either but you were absolutely correct.
My device was keeping track of my steps, my app was not. Turns out I had to force that to sync with my device. All is good now.
It's good to have someone knowledgeable of all this electronic wizardry point me in the right direction when something goes awry.