I wouldn't worry to much about it. Your BF% can fluctuate a bit depending on how hydrated you are, what you ate and if you went to the toilet already.
Just stick to tracking once a day, and maybe use www.trendweight.com (it link to Fitbit) to see the general line your BF% is going. It takes away those minor fluctuations.
If I jump on and off the scale a few times in a row, my BF% changes a bit every time, like 0,5% or so. It's just measuring error, the scale remains an estimate.