OG high / FG high

Been using Beersmith for some time now, and feel I've got it pretty well dialed in.
However in my last three batches I've overshot my OG by 3 or 4 points.
My FG has also finished out higher by the same number of points.
Example: last batch estimated OG of 1.054. I hit 1.058
Estimated FG of 1.012. It finished at 1.016

I can simply adjust my BH efficiency, but I was wondering if this is normal?
I didn't think this relationship was linear?

Likely something has changes for the last 3 batches. What do the last 3 batches have in common that may have changed? Maybe your base malt or some change in your process? Also, I would check the calibration of your hydrometer, refractometer and thermometers too.
Another possibility this time of year is if the lower temperatures have an influence on temperatures or other things in your process.