Possible battery degradation?

Manually switching Modes will do that everytime. It (mode switching ) is so much different than just letting the car switch the modes automatically like it does normally. Depending on how and when the modes are switched manually, can change almost all the gauge readings in the car when compared to how the gauges look when the car is left in one mode to do it thing(s).

 

That answers that question. Without knowing what your commute is, you're usually better off leaving things default to what Toyota has programmed the vehicle.

I also have a mostly 90% freeway commute. I do one of two things in the morning:

On colder mornings, I start the car but I do not turn on the heat. As soon as you do, the engine turns on, so avoid if possible to maximize EV. I drive the 1-2 miles to the freeway entrance. As soon as I go over 62 mph, the engine is forced on and that's when I can turn on the heat. Driving this way I get 12+ EV miles estimated in the morning.

On warmer mornings, I do the same as above driving to the freeway. I then stay in the right lane and keep my speed below 62 mph so the engine never turns on. Semis usually drive slower than this so I am not slowing down anyone except idiots who speed in the right lanes. This uses up EV a lot faster and I get <10 miles EV estimated. When new, I was getting 11+ but this has degraded over 150k. This is the true EV range as engine does not turn on. I don't get to turn on heat until 15 or so minutes after starting my commute, so honestly, I don't do this very often anymore as the bones have been aching in my old age.

Notice I don't touch the EV button in either case. I change my driving style and let Toyota determine what is most efficient.

 

same here

 

Your Hwy stats look excellent for a PiP and the 5-7 EV miles at 62mph looks about right too, remembering the few times I took the Hwy in EV. with the 2014 PiP.
I'm not sure about this as a reason that EV range drops so fast for you, but I think it might be cause your EV range is so elevated, compared to what is normal, and also the manual mode switching, it takes time for the computers to adjust to all EV operation. It doesn't just happen real time, due to history data.
I'd think that the computers need to start from scratch when you're driving EV only and add history data from each EV only drive. Than keep your fingers crossed that the EV only drive data doesn't get pushed way back into long term memory ( for lack of a better description ), every time you run Hwy switching modes again.

At least that is my theory from what I see with the Prime.

DrPrius has two different pack tests. Did you run one of those test from the DrPrius app? the one in your original post where the ICE stated early and the results were 17%?

 

If you haven't seen these tutorials yet. see if they are helpful. The vids are using a gen 4 so you have to adjust some things for the PiP, but they give a good general description of HowTo do the tests.
full pack diagnostic ---- youtu.be/hCf_vsgNRic
life expectancy test ---- youtu.be/AhfIbLkEq8w

and the DrPrius page
Hybrid battery diagnostic and repair tool for Toyota and Lexus
both videos are there too just scroll down the page and you'll see them and the other ones Jack and his crew have posted.

another life expectancy test - this time for a Gen 3 so some adjustments needed when testing the PiP
youtu.be/J5sjeMnwSFw