I'm guessing the Hybrid was a last minute thing and not being in the que for the HUGE demand for lithium batteries all they could get was nickel-metal hydride battery batteries, and put them under the seat.
Brand new design and they put the batteries under the back seat for the hybrid? What? No worries, no-one really cares about under seat storage or a flat floor in the back seat and most folks LOVE batteries in the passenger compartment, right?. ;) When a manufacturer takes a 15 year dirt nap...
It is working as designed. The blue bar graph is instantaneous MPG from the ICE. The white bar on the blue bar graph is the average MPG, (same as the white digital average right above the graph). As always if you reset the MPG by holding the OK button, it will take some miles for the average...